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/[slug]/page.tsx

@@ -4,6 +4,7 @@ import Link from 'next/link';
 import { useParams } from 'next/navigation';
 import Header from '@/components/Header';
 import Footer from '@/components/Footer';
+import { createClient } from '@/lib/supabase/client';
 
 interface ForumCategory {
   id: string;
@@ -173,8 +174,14 @@ export default function ForumCategoryPage() {
   const [showNewThread, setShowNewThread] = useState(false);
   const [newTitle, setNewTitle] = useState('');
   const [newBody, setNewBody] = useState('');
-  const [newAuthor, setNewAuthor] = useState('');
   const [submitting, setSubmitting] = useState(false);
+  const [newError, setNewError] = useState<string | null>(null);
+  const [isAuthenticated, setIsAuthenticated] = useState(false);
+
+  useEffect(() => {
+    const supabase = createClient();
+    supabase.auth.getUser().then(({ data: { user } }) => setIsAuthenticated(!!user));
+  }, []);
 
   const [search, setSearch] = useState('');
   const [debouncedSearch, setDebouncedSearch] = useState('');
@@ -228,6 +235,7 @@ export default function ForumCategoryPage() {
     e.preventDefault();
     if (!newTitle.trim() || !newBody.trim() || !category) return;
     setSubmitting(true);
+    setNewError(null);
     try {
       const res = await fetch('/api/forum/threads', {
         method: 'POST',
@@ -236,19 +244,24 @@ export default function ForumCategoryPage() {
           category_id: category.id,
           title: newTitle,
           body: newBody,
-          author_name: newAuthor || 'Anonymous',
         }),
       });
       const data = await res.json();
+      if (!res.ok) {
+        if (res.status === 401) {
+          window.location.href = `/forum/login?next=${encodeURIComponent(window.location.pathname)}`;
+          return;
+        }
+        throw new Error(data.error || `Failed (${res.status})`);
+      }
       if (data.thread) {
         setThreads(prev => [data.thread, ...prev]);
         setNewTitle('');
         setNewBody('');
-        setNewAuthor('');
         setShowNewThread(false);
       }
-    } catch {
-      // silent
+    } catch (err: any) {
+      setNewError(err.message || 'Failed to create thread. Please try again.');
     } finally {
       setSubmitting(false);
     }
@@ -282,29 +295,31 @@ export default function ForumCategoryPage() {
                   )}
                 </div>
               </div>
-              <button
-                onClick={() => setShowNewThread(!showNewThread)}
-                className="flex-shrink-0 bg-[#3b82f6] hover:bg-[#2563eb] text-white font-body font-semibold text-sm px-4 py-2 rounded-lg transition-colors"
-              >
-                + New Thread
-              </button>
+              {isAuthenticated ? (
+                <button
+                  onClick={() => setShowNewThread(!showNewThread)}
+                  className="flex-shrink-0 bg-[#3b82f6] hover:bg-[#2563eb] text-white font-body font-semibold text-sm px-4 py-2 rounded-lg transition-colors"
+                >
+                  + New Thread
+                </button>
+              ) : (
+                <Link
+                  href={`/forum/login?next=${typeof window === 'undefined' ? '/forum' : encodeURIComponent(window.location.pathname)}`}
+                  className="flex-shrink-0 bg-[#3b82f6] hover:bg-[#2563eb] text-white font-body font-semibold text-sm px-4 py-2 rounded-lg transition-colors"
+                >
+                  Sign in to post
+                </Link>
+              )}
             </div>
           </div>
         </div>
 
         <div className="max-w-container mx-auto px-4 py-6">
-          {/* New Thread Form */}
-          {showNewThread && (
+          {/* New Thread Form — auth-gated */}
+          {showNewThread && isAuthenticated && (
             <form onSubmit={handleNewThread} className="bg-[#1a2535] border border-[#2a3a50] rounded-lg p-5 mb-6">
               <h3 className="text-white font-heading font-semibold mb-4">Start a New Thread</h3>
               <div className="space-y-3">
-                <input
-                  type="text"
-                  placeholder="Your name (optional)"
-                  value={newAuthor}
-                  onChange={e => setNewAuthor(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]"
-                />
                 <input
                   type="text"
                   placeholder="Thread title *"
@@ -321,6 +336,11 @@ export default function ForumCategoryPage() {
                   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"
                 />
+                {newError && (
+                  <div className="bg-[#2a0a0a] border border-[#cc0000] text-[#ff8a8a] font-body text-sm px-3 py-2 rounded">
+                    {newError}
+                  </div>
+                )}
                 <div className="flex gap-3">
                   <button
                     type="submit"