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/templates/_card.html

@@ -1,17 +1,24 @@
 {{define "card"}}
 <a href="{{.Story.ArticleURL}}" target="_blank" rel="noopener noreferrer"
-   class="group block rounded-3xl bg-[color:var(--card)] border-2 border-[color:var(--ink)]/10 shadow-pete overflow-hidden hover:-translate-y-1 hover:shadow-pete-lg transition">
+   class="group block rounded-3xl bg-[color:var(--card)] border-2 {{if .Story.Posted}}border-theme-{{.Theme}} glow-theme-{{.Theme}}{{else}}border-[color:var(--ink)]/10{{end}} shadow-pete overflow-hidden hover:-translate-y-1 hover:shadow-pete-lg transition">
   {{if .Story.ImageURL}}
   <div class="aspect-[16/10] w-full overflow-hidden bg-[color:var(--ink)]/5">
-    <img src="{{.Story.ImageURL}}" alt="" loading="lazy"
+    <img src="{{thumb .Story.ImageURL}}" alt="" loading="lazy" decoding="async"
          class="h-full w-full object-cover group-hover:scale-105 transition duration-500">
   </div>
   {{end}}
   <div class="p-4 space-y-2">
-    <div class="flex items-center gap-2 text-xs">
+    <div class="flex items-center gap-2 text-xs flex-wrap">
+      {{if .ShowChannel}}{{$ch := channel .Story.Channel}}
+      <span class="inline-flex items-center rounded-full bg-theme-{{$ch.Theme}} text-white px-2.5 py-0.5 font-semibold uppercase tracking-wider">
+        <span aria-hidden="true" class="mr-1">{{$ch.Emoji}}</span>{{$ch.Title}}
+      </span>
+      <span class="text-[color:var(--ink)]/60 font-semibold">{{.Story.Source}}</span>
+      {{else}}
       <span class="inline-flex items-center rounded-full bg-theme-{{.Theme}} text-white px-2.5 py-0.5 font-semibold uppercase tracking-wider">
         {{.Story.Source}}
       </span>
+      {{end}}
       <span class="text-[color:var(--ink)]/50">{{timeAgo .Story.SeenAt}}</span>
     </div>
     <h3 class="font-display text-lg font-semibold leading-snug group-hover:underline underline-offset-2 decoration-theme-{{.Theme}}">