feat: file upload retry, secure file tokens, UI polish

- Add HMAC-based file token auth for secure AI model file access
- Add file upload retry with exponential backoff (max 3 retries)
- File endpoint now requires session auth or signed token
- Support assistant role messages in chat input
- Optimistic UI for attachments on message send
- Verify topic ownership before allowing messages
- Switch web scraping to Firecrawl API
- Agent profile page layout fixes (proper flex overflow)
- Add quick switcher (Ctrl+K) to sidenav
- Clean up longcat.ts and stale comments

server/api/upload/presigned.post.ts

@@ -39,7 +39,22 @@ export default defineEventHandler(async (event) => {
         responseChecksumValidation: 'WHEN_REQUIRED',
     });
 
-    const key = `veridian__uploads/${Date.now()}-${file.name.replace(/[^a-zA-Z0-9.]/g, '_')}-${event.context.user!.id}`
+    const fileParts = file.name.split('.');
+    if (fileParts.length < 2) {
+        throw createError({
+            statusCode: 400,
+            statusMessage: 'Invalid file name',
+            data: {
+                code: 'INVALID_FILE_NAME',
+                ok: false,
+            }
+        });
+    }
+
+    const fileExt = fileParts.pop()!;
+    const fileName = fileParts.join('.').replace(/[^a-zA-Z0-9.]/g, '_');
+
+    const key = `veridian__uploads/${Date.now()}-${fileName}-${event.context.user!.id}.${fileExt}`;
 
     const command = new PutObjectCommand({
         ACL: 'public-read',