forum: require auth for posting + add login/register/edit pages

- API: require auth on thread+reply POST (401 if !user); lazy-create
  forum_user_profile via service-role; author_name = display_name
- UI: surface API errors (kill silent catch); auto-redirect to login
  on 401; gate new-thread + reply forms with "Sign in to post" CTA
- /forum/login + /forum/register: forum-themed Supabase Auth pages
  with ?next= redirect support
- /forum/profile/edit + /api/forum/profile/me: edit own forum profile
  (username, display_name, bio, role, company, location, avatar)
- Header: logout button + sign-in/join links when not authed
- forum/user/[username]: show Edit Profile button when viewing own

Fixes posting bug: RLS rejected anon inserts with cryptic message
that the UI silently swallowed; now blocked with friendly 401 + redirect.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -194,8 +194,8 @@ export default function ForumThreadPage() {
 
   // Reply form
   const [replyBody, setReplyBody] = useState('');
-  const [replyAuthor, setReplyAuthor] = useState('');
   const [submitting, setSubmitting] = useState(false);
+  const [replyError, setReplyError] = useState<string | null>(null);
 
   // AI assistant
   const [aiQuestion, setAiQuestion] = useState('');
@@ -230,6 +230,7 @@ export default function ForumThreadPage() {
     e.preventDefault();
     if (!replyBody.trim() || !threadId) return;
     setSubmitting(true);
+    setReplyError(null);
     try {
       const res = await fetch('/api/forum/replies', {
         method: 'POST',
@@ -237,18 +238,23 @@ export default function ForumThreadPage() {
         body: JSON.stringify({
           thread_id: threadId,
           body: replyBody,
-          author_name: replyAuthor || 'Anonymous',
         }),
       });
       const data = await res.json();
+      if (!res.ok) {
+        if (res.status === 401) {
+          window.location.href = `/forum/login?next=${encodeURIComponent(window.location.pathname)}`;
+          return;
+        }
+        throw new Error(data.error || `Reply failed (${res.status})`);
+      }
       if (data.reply) {
         setReplies(prev => [...prev, data.reply]);
         setReplyBody('');
-        setReplyAuthor('');
         setTimeout(() => repliesEndRef.current?.scrollIntoView({ behavior: 'smooth' }), 100);
       }
-    } catch {
-      // silent
+    } catch (err: any) {
+      setReplyError(err.message || 'Failed to post reply. Please try again.');
     } finally {
       setSubmitting(false);
     }
@@ -468,18 +474,11 @@ export default function ForumThreadPage() {
               )}
             </div>
 
-            {/* Reply Form */}
-            {thread.status !== 'closed' && (
+            {/* Reply Form — auth-gated */}
+            {thread.status !== 'closed' && isAuthenticated && (
               <div className="bg-[#1a1a1a] border border-[#252525] rounded-lg p-5">
                 <h3 className="text-white font-heading font-semibold mb-4">Post a Reply</h3>
                 <form onSubmit={handleReply} className="space-y-3">
-                  <input
-                    type="text"
-                    placeholder="Your name (optional)"
-                    value={replyAuthor}
-                    onChange={e => setReplyAuthor(e.target.value)}
-                    className="w-full bg-[#111] border border-[#333] rounded-lg px-3 py-2 text-white font-body text-sm placeholder-[#555] focus:outline-none focus:border-[#3b82f6]"
-                  />
                   <textarea
                     placeholder="Share your thoughts, experience, or answer..."
                     value={replyBody}
@@ -488,6 +487,11 @@ export default function ForumThreadPage() {
                     rows={5}
                     className="w-full bg-[#111] border border-[#333] rounded-lg px-3 py-2 text-white font-body text-sm placeholder-[#555] focus:outline-none focus:border-[#3b82f6] resize-none"
                   />
+                  {replyError && (
+                    <div className="bg-[#2a0a0a] border border-[#cc0000] text-[#ff8a8a] font-body text-sm px-3 py-2 rounded">
+                      {replyError}
+                    </div>
+                  )}
                   <button
                     type="submit"
                     disabled={submitting || !replyBody.trim()}
@@ -499,6 +503,29 @@ export default function ForumThreadPage() {
               </div>
             )}
 
+            {thread.status !== 'closed' && !isAuthenticated && (
+              <div className="bg-[#0d1f35] border border-[#1e3a5f] rounded-lg p-5 text-center">
+                <h3 className="text-white font-heading font-semibold mb-1">Join the discussion</h3>
+                <p className="text-[#7a9ab8] font-body text-sm mb-4">
+                  Sign in or create a free account to post replies.
+                </p>
+                <div className="flex items-center justify-center gap-3">
+                  <Link
+                    href={`/forum/login?next=${encodeURIComponent(`/forum/thread/${threadId}`)}`}
+                    className="bg-[#3b82f6] hover:bg-[#2563eb] text-white font-body font-semibold text-sm px-5 py-2 rounded-lg transition-colors"
+                  >
+                    Sign In
+                  </Link>
+                  <Link
+                    href={`/forum/register?next=${encodeURIComponent(`/forum/thread/${threadId}`)}`}
+                    className="border border-[#3b82f6] text-[#3b82f6] hover:bg-[#3b82f6]/10 font-body font-semibold text-sm px-5 py-2 rounded-lg transition-colors"
+                  >
+                    Register
+                  </Link>
+                </div>
+              </div>
+            )}
+
             {thread.status === 'closed' && (
               <div className="bg-[#1a1a1a] border border-[#333] rounded-lg p-4 text-center text-[#666] font-body text-sm">
                 This thread is closed to new replies.