feat(brand): redraw brand icon from Inkscape source and regenerate all favicon assets

[gnacho]

Redraw brand icon source (Inkscape) and regenerate all derived favicon / PWA assets

Context

The brand icon has been redrawn by hand in Inkscape as a standalone SVG (nearly square
viewport, motif touching all edges, single fill color). Today the app derives every favicon
and PWA asset from the old traced masters (logo-square.svg / logo.svg).

Goal

• Use the new SVG as the single source of truth for the brand mark.
• Replace the masters (logo-square.svg, logo.svg) keeping the current amber gradient
  (#FBBF24 -> #F97316), which must keep working on both light and dark themes.
• Regenerate every derived asset from the new master:
  • favicon-light.ico / favicon-dark.ico (16 + 32)
  • favicon-32.png
  • pwa-icon-192.png / pwa-icon-512.png
  • apple-touch-icon.png
  • icons/{claro,oscuro}/helios-icon-{32,180,192,512}.png
• Update the inline brand SVG used by the shell (BrandLogoIcon) so the in-app logo matches
  the new mark.

Verification

• Amber coverage measured on the new square master; no empty bands top/bottom in either theme.
• npm run build, lint, server tests all green; deployed favicon assets byte-identical
  between repo and prod.