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.

src/app/forum/thread/[id]/page.tsx

@@ -354,7 +354,7 @@ export default function ForumThreadPage() {
                 <Avatar name={thread.author_name} isAI={false} />
                 <div className="flex-1 min-w-0">
                   <div className="flex items-center gap-2 mb-2">
-                    <span className="text-white font-body font-semibold text-sm">{thread.author_name}</span>
+                    <Link href={`/forum/user/${encodeURIComponent(thread.author_name)}`} className="text-white font-body font-semibold text-sm hover:text-[#3b82f6] hover:underline">{thread.author_name}</Link>
                     <span className="text-[#555] font-body text-xs">·</span>
                     <span className="text-[#555] font-body text-xs">{timeAgo(thread.created_at)}</span>
                     <span className="text-[#555] font-body text-xs">·</span>
@@ -389,7 +389,7 @@ export default function ForumThreadPage() {
                         <Avatar name={reply.author_name} isAI={reply.is_ai_response} />
                         <div className="flex-1 min-w-0">
                           <div className="flex items-center gap-2 mb-2 flex-wrap">
-                            <span className="text-white font-body font-semibold text-sm">{reply.author_name}</span>
+                            <Link href={`/forum/user/${encodeURIComponent(reply.author_name)}`} className="text-white font-body font-semibold text-sm hover:text-[#3b82f6] hover:underline">{reply.author_name}</Link>
                             {reply.is_ai_response && (
                               <span className="text-xs bg-[#3b82f6]/20 text-[#3b82f6] border border-[#3b82f6]/30 px-2 py-0.5 rounded font-body font-semibold">
                                 AI Assistant