fix(showcase): remodel office-chair as a mesh task chair on a chair mat beside a snake plant

Beside the other new-category pieces the chair was among the weakest: tall
and thin (horizontal fill 0.27), a plain rounded seat slab in tangerine, a
flat dark mesh panel in a warm-white frame, and the floor/wall seam showing
through the mesh. It is rebuilt as a premium task chair in a desk-corner
vignette:

- a two-tone cushion in a moulded graphite shell: a woven muted-teal centre
  panel sculpted with a rear dish and two thigh channels, rolling over a
  waterfall front, mid-grey knit side panels, a piped welt in the seam
  groove and another on the top edge
- an elastomeric mesh (ribs over strands, open cells) stretched over a
  graphite frame that swells toward its foot; an S-curved lumbar pad on
  straps ending in two sliders clamped round the frame
- a mesh headrest in its own frame on the aluminium stem
- 4D arms: telescoping cover, height and pivot buttons, pad plate, pad
- a larger knurled tension knob; studio reflection term on aluminium,
  chrome, steel, graphite plastics and the mat (after espresso-machine)
- a smoked polycarbonate chair mat with a bevelled edge and desk lip, every
  caster pressed 0.6 mm into it; a snake plant (nine banded blades) in a
  speckled stone planter beside it
- a lower camera: the mesh back and headrest read against the dark wall,
  the seam sits behind the seat, the wedge pools right of the plant

Coplanar hygiene fixed by staggering parts, not by widening bands: welt
hexagons turned vertex-up, the mechanism top 1 mm under the cushion floor,
lumbar straps stopping 6 mm inside their sliders, leaf bases 1 mm deeper
each.

Budget changes:
- Base tris 35200-36800 -> 43700-45200 (measured 44440; LOD 0.5000/0.2200)
- Materials 9 -> 14, face floors per material; collider 551 (ceiling 580)
- Outer AABB -> (1.635, 1.480, 1.317) m; chair shells 80 -> 89
- Grounded (16) now: mat flat on the floor, every wheel pressed into the
  mat 0.3-1.0 mm (ray cast on the mat), pot on the floor
- New: lumbar sliders 2.0-6.5 mm off the frame tube (21, measured
  3.5-5.2 mm); leaves rooted 15-45 mm in the soil (22, 24.5-31.6 mm)
- Connectivity counts the chair's shells only (wheels press into the mat)
- Asset-quality remap moves from 21 to 23

Falsifiers (flag -> measured -> exit), all on the final code:
  --skip-decimate  LOD1 1.0000                              9
  --stray-vert     loose_v 1                               15
  --lift-z         zmin 0.05000                            16
  --float-caster   wheel sink -4.4 mm                      16
  --curl-mat       mat underside rises 6.0 mm              16
  --skew-spoke     spacing off 3.000 deg                   17
  --offset-column  3.0 mm off hub and socket axes          18
  --uneven-arms    arm mirror 10.0 mm                      19
  --loose-wheel    2 components                            20
  --float-lumbar   slider gap 0.07-11.0 mm                 21
  --float-leaves   leaf depth -15.5 to -8.4 mm             22
Every falsifier keeps the default AABB and 44440 tris.
tests/check_falsifier_targets.py --run --only office-chair passes.

Evidence (live runs, local):
- .scratch/5.2/blender-5.2.1-windows-x64/blender.exe (Blender 5.2.1 LTS).
  Two default runs exit 0 with identical measured lines and export size;
  hygiene all 0 including coplanar cross-shell pairs.
- Framing: fill x 0.491 (was 0.27), y 0.839; margins l .191 r .319
  b .072 t .089.
- Contact sheet: luma 0.2424 (calibration 0.2369-0.2428), stage 0.2220,
  warmth +0.101, sat 0.1892 (band 0.1525-0.2367); before sat 0.2393 (over
  band) from the tangerine seat.
- Asset sheet: before, a thin orange chair; now a detailed chair on a mat
  with a plant, not the least-designed object in the lineup (the hydrant
  is simpler). Honest note: at thumbnail the chair is dark and muted.
- build_gallery, check_site_links and every tests/check_*.py pass.
- 4.5 LTS and 5.1 were not run locally.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: TMHSDigital

README.md

@@ -151,7 +151,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
   <a href="showcase/quad-drone/"><img src="showcase/quad-drone/preview.webp" width="24%" alt="Quad drone: a white-and-graphite camera quadcopter on four carbon arms with red lock rings, twin-blade props, rubber-footed skids and a three-axis gimbal camera, on a dark studio floor" /></a>
   <a href="showcase/soccer-goal/"><img src="showcase/soccer-goal/preview.webp" width="24%" alt="Soccer goal: a white 5 by 2 m youth goal with sloped rear supports and a sagging diamond-mesh net edged in red rope, on a turf patch with a painted goal line, on a dark studio floor" /></a>
   <a href="showcase/fallen-log/"><img src="showcase/fallen-log/preview.webp" width="24%" alt="Fallen log: a mossy log settled into a soil mound, its dark furrowed bark peeled in patches, a hollow ringed butt, tiers of shelf fungi, toadstools, ferns and fallen leaves, on a dark studio floor" /></a>
-  <a href="showcase/office-chair/"><img src="showcase/office-chair/preview.webp" width="24%" alt="Office chair: a tangerine-upholstered mesh-back task chair with a headrest, T-arms, a chrome gas lift and a polished five-star base on twin-wheel casters, on a dark studio floor" /></a>
+  <a href="showcase/office-chair/"><img src="showcase/office-chair/preview.webp" width="24%" alt="Office chair: a graphite mesh-back task chair with a muted-teal two-tone seat, a mesh headrest and 4D armrests on a polished five-star base, standing on a smoked chair mat beside a snake plant in a stone planter" /></a>
   <a href="showcase/hover-bike/"><img src="showcase/hover-bike/preview.webp" width="24%" alt="Hover bike: a teal sci-fi speeder with pearl racing stripes, a stitched black saddle, clip-on bars and two ducted fans with orange spinners, parked on landing skids, on a dark studio floor" /></a>
   <a href="showcase/weight-rack/"><img src="showcase/weight-rack/preview.webp" width="24%" alt="Weight rack: a red half rack holding a barbell loaded with blue and yellow bumpers on J-hooks, plates on storage horns and two hex dumbbells, on a dark studio floor" /></a>
   <a href="showcase/boulder-cluster/"><img src="showcase/boulder-cluster/preview.webp" width="24%" alt="Boulder cluster: a speckled granite block, a banded sandstone boulder split in two and a slab resting on a smaller boulder, sunk in a grassy soil mound with pebbles and wildflowers, on a dark studio floor" /></a>
@@ -251,7 +251,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
 
 [`fallen-log`](showcase/fallen-log/) — the second `nature` piece: procedural fallen forest log (one furrowed lathe along a bowed axis, bark peeled to sapwood scored by beetle galleries, a rotted hollow saw-cut butt with growth rings, a splintered snapped top, broken branch stubs, moss cushions on the top and shaded side, three tiers of bracket fungi, a soil mound with toadstools, ferns and fallen leaves), whose bed along its length, brackets rooted in the bark, mass centre over its contact patch, moss on up- and shade-facing surfaces and ground cover rooted in the soil are recomputed from the mesh, through the same pipeline. Falsifiers `--hump-ground` exits 17, `--float-fungi` 18, `--tilt-ground` 19, `--sunny-moss` 20, `--float-litter` 21.
 
-[`office-chair`](showcase/office-chair/) — the second `household` piece: procedural ergonomic task chair (polished aluminium five-star base with ribbed spokes and five swivelled twin-wheel casters, a chrome gas lift in a telescoping cover under a tilt mechanism with knob and levers, a contoured upholstered seat with a piped welt, a reclined mesh back with a lumbar pad and headrest on an aluminium spine, height-adjustable T-arms), whose ten wheels on the floor, five-star spacing with plumb swivel stems on one circle, gas-lift column coaxial with hub and socket, mirrored level armrests with seat height and mass centre inside the caster contact hull, and single connected assembly are recomputed from the mesh, through the same pipeline. Falsifiers `--float-caster` exits 16, `--skew-spoke` 17, `--offset-column` 18, `--uneven-arms` 19, `--loose-wheel` 20.
+[`office-chair`](showcase/office-chair/) — the second `household` piece: procedural ergonomic task chair on a chair mat at a desk corner (polished aluminium five-star base with ribbed spokes and five swivelled hooded twin-wheel casters, a chrome gas lift in a telescoping cover under a synchro-tilt mechanism with tension knob and paddles, a two-tone sculpted cushion with thigh channels, a waterfall front and piped welts in a moulded shell, an elastomeric mesh back and mesh headrest on graphite frames with an S-curved lumbar pad on sliders, 4D armrests, a smoked polycarbonate mat and a snake plant in a stone planter), whose mat flat on the floor with every wheel pressed into it, five-star spacing with plumb swivel stems on one circle, gas-lift column coaxial with hub and socket, mirrored level armrests with seat height and mass centre inside the caster contact hull, single connected chair, lumbar sliders clamped on the frame and leaves rooted in the soil are recomputed from the mesh, through the same pipeline. Falsifiers `--float-caster` and `--curl-mat` exit 16, `--skew-spoke` 17, `--offset-column` 18, `--uneven-arms` 19, `--loose-wheel` 20, `--float-lumbar` 21, `--float-leaves` 22.
 
 [`hover-bike`](showcase/hover-bike/) — the second `vehicles` piece: procedural sci-fi hover bike (a sculpted two-tone fuselage with panel seams, intake grilles, tail vents and cooling fins, a stitched pleated saddle, clip-on bars with grips, levers and an emissive instrument cluster, a flyscreen and headlight pod, two glowing exhaust nozzles, two ducted fans with canted stator vanes and handed seven-blade rotors, booms with foot pegs, and two landing skids on struts), whose skids on the floor, rotor hubs coaxial with their shrouds, blade-tip clearance to the shroud wall, mirror-symmetric fuselage with seat height, equal blade spacing, mass centre inside the skids' contact polygon and single connected assembly are recomputed from the mesh, through the same pipeline. Falsifiers `--float-skid` exits 16, `--offset-hub` 17, `--long-blades` 18, `--odd-hull` 19, `--skew-blade` 20, `--narrow-skids` 21, `--pop-lens` 22.