docs: the architecture diagram fits its boxes and nothing collides

Widen node boxes, balance the four regions and row spacing, and align
SQL above Caller. Route schemas around the perimeter, separate the
tables and differential paths, and move labels and numbered badges
clear of borders, text and unrelated edges.

Preserve every component, edge, fact and step number. No labels were
cut; only the caller note gains a line break. The generator is unchanged.
Verified through four render/gate/visual rounds, a final GATE PASS,
and exact checks for edge crossings and badge placement.

Author: Aly700