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/pages/agent/[id]/index.vue

@@ -1,4 +1,5 @@
 <script setup lang="ts">
+import { nanoid } from 'nanoid';
 import type { BaseMessage } from '~/composables/useChat';
 import type { ModelWithProvider } from '~/composables/useModels';
 
@@ -43,7 +44,23 @@ const handleSubmit = async (message: BaseMessage, model: ModelWithProvider | nul
         children: [],
         generationId: null,
         activeChildId: null,
-        attachments: [],
+        attachments: message.files?.map(file => ({
+            id: nanoid(),
+            userId: user.value!.id,
+            topicId: '',
+            messageId: '',
+            fileId: file.id,
+            createdAt: new Date(),
+            file: {
+                id: file.id,
+                userId: user.value!.id,
+                name: file.name,
+                mimeType: file.mimeType,
+                size: file.size ?? 0,
+                url: file.url,
+                createdAt: new Date(),
+            },
+        })) ?? [],
         deleted: false,
         createdAt: new Date(),
         updatedAt: new Date(),
@@ -75,6 +92,27 @@ const handleSubmit = async (message: BaseMessage, model: ModelWithProvider | nul
 
     return startGeneration(model, undefined, route.params.id as string);
 };
+
+const handleAddMessage = async (message: BaseMessage, role: 'user' | 'assistant', _model: ModelWithProvider | null) => {
+    const user = useAuth().user;
+    if (!user) {
+        console.error('No user');
+        return;
+    }
+
+    const topic = await createTopic(agent.value!.id);
+    if (!topic) throw new Error('Failed to create topic');
+
+    const { sendMessage } = await useChat(topic.id, false);
+
+    const res = await sendMessage(message, undefined, role);
+    if (res.ok === false) {
+        console.error('Failed to send message:', res.error);
+        return;
+    }
+
+    await navigateTo(`/agent/${route.params.id}/topic/${topic.id}`);
+};
 </script>
 
 
@@ -108,7 +146,8 @@ const handleSubmit = async (message: BaseMessage, model: ModelWithProvider | nul
 
                 <div class="sticky bottom-0 z-10 bg-[var(--bg-surface)] pb-4 w-full rounded-t-2xl">
                     <ChatInput v-model="inputValue" class="[view-transition-name:chat-prompt] duration-150 ease-in-out"
-                        :agent="agent" :providers="providers?.filter(p => p.enabled)" @submit="handleSubmit" />
+                        :allow-manual-role="true" :agent="agent" :providers="providers?.filter(p => p.enabled)"
+                        @submit="handleSubmit" @add-message="handleAddMessage" />
                 </div>
             </div>
         </div>