feat(icon): redesign app icon as "Beacon" and ship multi-resolution ICO

- Replace generic Spotify-green circle with a refined "Beacon" design:
  squircle + deep-teal diagonal gradient (#0B3D3B → #1A6B5E) + warm
  parchment play triangle (#F5F1E8) with drop shadow, top sheen, and
  ghosted echo-chevrons hinting at broadcast/stream
- Grow icon.ico from a single 16×16 frame (208 B) to a 10-frame
  multi-resolution ICO (16/20/24/32/40/48/64/96/128/256, ~37 KB) so
  Windows no longer upscales 16×16 into mush for the installer chrome,
  Start Menu, desktop shortcuts, Alt+Tab, and File Explorer tiles
- Add scripts/generate-icon.py: SVG is the source of truth; resvg-py
  rasterizes every ICO size; Pillow packs the multi-resolution ICO
- Update tray.py to pick a 64×64 frame from the new ICO and update its
  procedural fallback to the same Beacon palette so a missing ICO no
  longer regresses the tray to the old Spotify-green circle
- Add resvg-py to [dev] deps (build-time only)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pyproject.toml

@@ -69,6 +69,9 @@ dev = [
     "pytest-asyncio>=0.21",
     "httpx>=0.24",
     "ruff>=0.4.0",
+    # SVG -> PNG rasterizer used by scripts/generate-icon.py to (re)build
+    # media_server/static/icons/icon.ico from icon.svg. Build-time only.
+    "resvg-py>=0.3.2",
 ]
 
 [project.urls]