refactor(desktop): restructure pages and consolidate UI components

- Rename channels.tsx to clients.tsx
- Remove standalone skills.tsx and tools.tsx pages
- Add agent/ directory for agent-related pages
- Update layout and navigation structure
- Add tabs component to ui package
- Update fonts and global styles

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

apps/desktop/.env.example

@@ -0,0 +1,23 @@
+# =============================================================================
+# Multica Desktop Environment Configuration
+# =============================================================================
+#
+# Copy this file to create environment-specific configs:
+#   .env.development  - Local development (npm run dev)
+#   .env.staging      - Test environment (npm run build --mode staging)
+#   .env.production   - Production release (npm run build)
+#
+# Variable naming convention:
+#   MAIN_VITE_*       - Available in main process only
+#   RENDERER_VITE_*   - Available in renderer process only
+#   VITE_*            - Available in all processes
+#
+# =============================================================================
+
+# Gateway WebSocket server URL
+# Used for Hub <-> Gateway communication
+MAIN_VITE_GATEWAY_URL=http://localhost:3000
+
+# Multica API server URL
+# Used for HTTP API requests (auth, updates, etc.)
+MAIN_VITE_MULTICA_URL=http://localhost:3001