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>

media_server/static/icons/icon.svg

@@ -1,10 +1,33 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256" role="img" aria-label="Media Server">
   <defs>
-    <linearGradient id="grad" x1="0%" y1="0%" x2="100%" y2="100%">
-      <stop offset="0%" style="stop-color:#1db954;stop-opacity:1" />
-      <stop offset="100%" style="stop-color:#1ed760;stop-opacity:1" />
+    <linearGradient id="bg" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%"  stop-color="#0B3D3B"/>
+      <stop offset="100%" stop-color="#1A6B5E"/>
     </linearGradient>
+    <linearGradient id="sheen" x1="50%" y1="0%" x2="50%" y2="100%">
+      <stop offset="0%"  stop-color="#FFFFFF" stop-opacity="0.18"/>
+      <stop offset="55%" stop-color="#FFFFFF" stop-opacity="0"/>
+    </linearGradient>
+    <filter id="triShadow" x="-20%" y="-20%" width="140%" height="140%">
+      <feGaussianBlur stdDeviation="3"/>
+      <feOffset dx="3" dy="5"/>
+      <feComponentTransfer><feFuncA type="linear" slope="0.45"/></feComponentTransfer>
+      <feMerge><feMergeNode/><feMergeNode in="SourceGraphic"/></feMerge>
+    </filter>
+    <clipPath id="clip"><rect x="0" y="0" width="256" height="256" rx="58" ry="58"/></clipPath>
   </defs>
-  <circle cx="50" cy="50" r="45" fill="url(#grad)"/>
-  <path fill="white" d="M35 25 L35 75 L75 50 Z"/>
+  <g clip-path="url(#clip)">
+    <rect width="256" height="256" fill="url(#bg)"/>
+    <rect width="256" height="256" fill="url(#sheen)"/>
+    <g stroke="#F5F1E8" stroke-width="4.6" stroke-linecap="round" stroke-linejoin="round" fill="none" opacity="0.18">
+      <polyline points="66,72 105,128 66,184"/>
+      <polyline points="85,82 124,128 85,174" opacity="0.6"/>
+    </g>
+    <path d="M88.3 55 L88.3 201 L193.3 128 Z"
+          fill="#F5F1E8"
+          stroke="#F5F1E8" stroke-width="9" stroke-linejoin="round"
+          filter="url(#triShadow)"/>
+  </g>
+  <rect x="0.5" y="0.5" width="255" height="255" rx="58" ry="58"
+        fill="none" stroke="#000000" stroke-opacity="0.18" stroke-width="1"/>
 </svg>