Error Feedback Service + friendly error handling across all pages

- Error Feedback Service: POST /api/feedback saves to JSONL, GET with admin token
- ErrorFeedback component: warm amber tones, friendly messages, 'Report Issue' button
- Replaced ALL red-themed error displays across 15+ pages with ErrorFeedback
- Kind classification: network, auth, location, upgrade, default messages
- QA test suite v2: 8-layer testing (system, API, render, scenario, edge, mobile, perf, security)
- Browser-based visual QA with Playwright (Layer 9)

src/app/forum/[threadId]/page.tsx

@@ -8,7 +8,6 @@ import {
   Crown,
   Star,
   Clock,
-  AlertTriangle,
   CheckCircle,
   Loader2,
   Lock,
@@ -16,6 +15,7 @@ import {
   ShieldCheck,
   Flag,
 } from "lucide-react";
+import ErrorFeedback from "@/components/ErrorFeedback";
 
 interface AuthorInfo {
   id: string;
@@ -206,16 +206,7 @@ export default function ThreadDetailPage() {
           <p className="text-sm text-gray-500">Loading thread...</p>
         </div>
       ) : error ? (
-        <div className="mx-4 mt-4 bg-red-900/10 border border-red-800/30 rounded-2xl p-6 text-center">
-          <AlertTriangle size={32} className="mx-auto text-red-400 mb-2" />
-          <p className="text-sm text-red-300">{error}</p>
-          <button
-            onClick={() => { fetchThread(); fetchPosts(); }}
-            className="mt-3 text-xs text-[#D4AF37] underline"
-          >
-            Try again
-          </button>
-        </div>
+        <ErrorFeedback error={error} kind="network" onRetry={() => { fetchThread(); fetchPosts(); }} context="thread posts" />
       ) : !thread ? (
         <div className="mx-4 mt-4 bg-gray-900/40 border border-gray-800/60 rounded-2xl p-6 text-center">
           <p className="text-sm text-gray-400">Thread not found</p>
@@ -384,9 +375,7 @@ export default function ThreadDetailPage() {
                 </div>
 
                 {replyError && (
-                  <div className="bg-red-900/10 border border-red-800/30 rounded-xl p-3">
-                    <p className="text-xs text-red-300">{replyError}</p>
-                  </div>
+                  <ErrorFeedback error={replyError} kind="default" onRetry={() => setReplyError(null)} context="reply" />
                 )}
               </form>
             )}