feat: Improve UI layout and navigation

- Increase logo size (48x48 desktop, 56x56 mobile) for better visibility
- Add logo as favicon
- Add logo to mobile header
- Move user menu to navigation bars (sidebar on desktop, bottom bar on mobile)
- Fix desktop chat layout - container structure prevents voice controls cutoff
- Fix mobile bottom bar - use icon-only ActionIcons instead of truncated text buttons
- Hide Create Node/New Conversation buttons on mobile to save header space
- Make fixed header and voice controls work properly with containers

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

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

package.json

@@ -23,6 +23,7 @@
     "@react-three/drei": "latest",
     "@react-three/fiber": "latest",
     "@tabler/icons-react": "^3.35.0",
+    "@xstate/react": "^6.0.0",
     "ai": "latest",
     "jsonwebtoken": "latest",
     "next": "latest",
@@ -32,9 +33,11 @@
     "surrealdb": "latest",
     "three": "latest",
     "umap-js": "latest",
+    "xstate": "^5.24.0",
     "zod": "latest"
   },
   "devDependencies": {
+    "@playwright/test": "^1.56.1",
     "@types/jsonwebtoken": "latest",
     "@types/node": "latest",
     "@types/react": "latest",