Web UI: music channel, posted-to-Matrix glow, redesigned index, AVIF thumbnails

- Add music as a fourth channel (nav + theme color)
- Glowing themed border on cards that have been posted to Matrix
- Replace per-channel index sections with: "Pete just posted" strip,
  channel dashboard (last post, 24h count, totals), unified latest feed
- /img proxy: SSRF-guarded thumbnail re-encoder that resizes to 800px
  and runs avifenc -q 45, cached under data/img-cache

internal/web/static/css/input.css

@@ -58,18 +58,33 @@ html[data-phase="night"] {
   .bg-theme-gaming    { background-color: #4caf7d; }
   .bg-theme-tech      { background-color: #5aa9e6; }
   .bg-theme-politics  { background-color: #e07a5f; }
+  .bg-theme-music     { background-color: #b079d6; }
 
   .text-theme-gaming    { color: #2d8a5a; }
   .text-theme-tech      { color: #2f7fb8; }
   .text-theme-politics  { color: #b8523a; }
+  .text-theme-music     { color: #8a4fb8; }
 
   .decoration-theme-gaming    { text-decoration-color: #4caf7d; }
   .decoration-theme-tech      { text-decoration-color: #5aa9e6; }
   .decoration-theme-politics  { text-decoration-color: #e07a5f; }
+  .decoration-theme-music     { text-decoration-color: #b079d6; }
 
   .border-theme-gaming    { border-color: #4caf7d; }
   .border-theme-tech      { border-color: #5aa9e6; }
   .border-theme-politics  { border-color: #e07a5f; }
+  .border-theme-music     { border-color: #b079d6; }
+
+  /* "Posted to Matrix" glow — soft pulsing aura in the channel's theme color. */
+  .glow-theme-gaming   { box-shadow: 0 0 0 2px rgba(76,175,125,0.35), 0 0 24px 4px rgba(76,175,125,0.45); animation: pete-glow-pulse 2.4s ease-in-out infinite; }
+  .glow-theme-tech     { box-shadow: 0 0 0 2px rgba(90,169,230,0.35), 0 0 24px 4px rgba(90,169,230,0.45); animation: pete-glow-pulse 2.4s ease-in-out infinite; }
+  .glow-theme-politics { box-shadow: 0 0 0 2px rgba(224,122,95,0.35), 0 0 24px 4px rgba(224,122,95,0.45); animation: pete-glow-pulse 2.4s ease-in-out infinite; }
+  .glow-theme-music    { box-shadow: 0 0 0 2px rgba(176,121,214,0.35), 0 0 24px 4px rgba(176,121,214,0.45); animation: pete-glow-pulse 2.4s ease-in-out infinite; }
+
+  @keyframes pete-glow-pulse {
+    0%, 100% { filter: brightness(1); }
+    50%      { filter: brightness(1.08); }
+  }
 
   .line-clamp-3 {
     display: -webkit-box;