perf: Add performance optimizations and Tanuki avatar

Frontend:
- Add memoization to MessageList with custom comparison function
- Implement incremental caching for processedMessages to avoid O(n) rebuilds during streaming
- Wrap Message component with memo()
- Add better error handling for file uploads in SessionContext

Backend:
- Improve upload error handling with proper response checks

Infrastructure:
- Add client_max_body_size 100m to nginx for file uploads
- Add Tanuki avatar (optimized 256x256, 77KB)

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

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

backend/server.js

@@ -175,7 +175,9 @@ app.get('/api/hosts', requireAuth, (req, res) => {
     color: host.color,
     icon: host.icon,
     connectionType: host.connection.type,
-    isLocal: host.connection.type === 'local'
+    isLocal: host.connection.type === 'local',
+    basePaths: host.basePaths || [],
+    defaultPath: host.basePaths?.[0] || '/home'
   }));
   res.json({ hosts, defaultHost: hostsConfig.defaults?.host || 'neko' });
 });