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

app/components/Attachment/Preview.vue

@@ -8,11 +8,13 @@ const props = defineProps<{
         mimeType: string;
         status: 'uploading' | 'uploaded' | 'error';
         url: string;
+        retryCount?: number;
     }
 }>();
 
 const emit = defineEmits<{
     delete: [];
+    retry: [];
 }>();
 
 const handleDelete = async () => {
@@ -21,12 +23,16 @@ const handleDelete = async () => {
 </script>
 
 <template>
-    <div class="relative h-full w-fit flex">
-        <Display :file="props.file" />
+    <div class="relative h-full w-fit flex flex-shrink-0">
+        <Display :file="props.file" @retry="emit('retry')" />
 
         <button @click="handleDelete"
             class="absolute top-0 right-0 translate-x-1/2 -translate-y-1/2 flex items-center justify-center w-4 h-4 rounded-full bg-[var(--bg-base)] border border-[var(--color-border)] text-xs text-[#ff3b3b]">
             <span class="i-mynaui-x text-3"></span>
         </button>
+        <div v-if="file.status === 'error'"
+            class="absolute bottom-0 right-0 translate-x-1/4 translate-y-1/4 flex items-center justify-center w-4 h-4 rounded-full bg-red-500">
+            <span class="i-mynaui-danger-triangle text-2.5 text-white"></span>
+        </div>
     </div>
 </template>