feat: Major UI improvements and SSH-only mode

- Tool rendering: Unified tool_use/tool_result cards with collapsible results
- Special rendering for WebSearch, WebFetch, Task, Write tools
- File upload support with drag & drop
- Permission dialog for tool approvals
- Status bar with session stats and permission mode toggle
- SSH-only mode: Removed local container execution
- Host switching disabled during active session with visual indicator
- Directory browser: Browse remote directories via SSH
- Recent directories dropdown with localStorage persistence
- Follow-up messages during generation
- Improved scroll behavior with "back to bottom" button

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/package.json

@@ -12,6 +12,7 @@
     "express": "^4.18.2",
     "ws": "^8.14.2",
     "cors": "^2.8.5",
-    "uuid": "^9.0.0"
+    "uuid": "^9.0.0",
+    "multer": "^1.4.5-lts.1"
   }
 }