forum: user profile pages + clickable bylines + neon pulse favicon

USER PROFILES (/forum/user/[username]):
- New API at /api/forum/user-by-username/[username] resolves by
  username OR display_name (URL-encoded), since forum threads/replies
  store author_name = display_name. Returns the persona's profile,
  thread history (up to 50), and recent replies (up to 20).
- New page renders the persona card with archetype badge
  (Audio Engineer / Colorist / etc.) + expertise level badge
  (beginner/intermediate/senior) + role title, company, location,
  years_experience, join date, and an expertise-tags chip row.
- Two columns underneath: "Threads started" and "Recent replies"
  with proper deep-links into each thread.
- Author names in /forum, /forum/[slug], and /forum/thread/[id] are
  now <Link> elements pointing to /forum/user/<displayname>, with
  onClick=stopPropagation so the card-level click handler doesn't
  also fire.

FAVICON:
- Hand-built neon pulse waveform — emerald→cyan→purple gradient on
  dark navy background, designed to read at 16×16 to 256×256.
- Multi-resolution favicon.ico (16/32/48/64) + SVG + PNGs at
  16/32/48/64/96/192/256 under /static/favicons/.
- layout.tsx icons block now references all sizes including the
  apple-touch sizes (192, 256).

No env / DB changes here — pure deploy.

public/static/favicons/favicon.svg

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256">
+  <defs>
+    <!-- Diagonal cyan→emerald sweep with a purple highlight on the peak -->
+    <linearGradient id="g" x1="0%" y1="0%" x2="100%" y2="100%">
+      <stop offset="0%"  stop-color="#00d4ff"/>
+      <stop offset="55%" stop-color="#00ff9f"/>
+      <stop offset="100%" stop-color="#c400ff"/>
+    </linearGradient>
+    <!-- subtle glow for the peak so the icon reads at 16px -->
+    <filter id="glow" x="-20%" y="-20%" width="140%" height="140%">
+      <feGaussianBlur stdDeviation="3" result="b"/>
+      <feMerge><feMergeNode in="b"/><feMergeNode in="SourceGraphic"/></feMerge>
+    </filter>
+  </defs>
+
+  <!-- Rounded-square dark background -->
+  <rect x="0" y="0" width="256" height="256" rx="44" fill="#050a08"/>
+
+  <!-- Pulse / waveform: a tight ECG-style spike that reads as "beat".
+       The shape is intentionally bold and asymmetric so the silhouette
+       survives 16×16 antialiasing. -->
+  <g fill="none" stroke="url(#g)" stroke-width="22" stroke-linecap="round"
+     stroke-linejoin="round" filter="url(#glow)">
+    <path d="M 24 140
+             L 78 140
+             L 100 92
+             L 122 200
+             L 144 60
+             L 166 168
+             L 188 140
+             L 232 140"/>
+  </g>
+</svg>