feat: regenerate all brand assets from the circular-H icon

[FAZuH]

What

One approved SVG (assets/hyprlay.svg) is now the single source for every brand asset:

• scripts/gen_tray_icons.py rewritten to rasterize it via rsvg-convert (validated pixel-exact against the approved renders) and emit: tray pair (48×48, disconnected = H-only dim to #a0a0a0, mirroring the old convention), hyprlay-{48,64,128,256}.png, and hyprlay.ico (Pillow ICO save; same size set {256,128,64,48,32,16}, PNG-compressed entries — 370 KB → 25 KB).
• All 8 assets regenerated to the new circular-H design (black disc, dark-grey ring at 5% of diameter, bold white H as a font-independent path).
• README banner updates automatically (it embeds hyprlay-64.png).
• Zero Rust behavior changes — include_bytes! paths already matched; only a stale module comment in src/platform/icon.rs updated.
• CHANGELOG: user-facing entry under [Unreleased] / Platforms.

Verification

• Generated rasters pixel-exact vs the approved design renders; regen after review edits byte-identical.
• CI-exact sequence green locally (fmt / clippy -D warnings / 307 tests) — offload host unreachable today, ran the mirror locally.
• Live: tray unit restarted with the new icon (SNI pixmap verified), daemon relaunched and connected, user config untouched.

Design approved by the user 2026-09-11 (approval gate passed before wiring).

[github-actions]

Release Preview

Next version: v0.3.1

0.3.1 (2026-09-11)

Platforms

• Changed the app and tray icon to a circular design
• Fixed source installs failing on a fresh dependency resolution