feat(ui): command palette, activity log, data export, fullscreen, connection status

[natiixnt]

Summary

• Command Palette (Ctrl+K / Cmd+K) - fuzzy search across all tabs and actions, keyboard navigation, SVG icons
• Activity Log (L key) - real-time system event log with console interception, filter by type (info/warning/error/connection), resizable panel, clear button
• Data Export (E key) - export buffered sensor data as JSON or CSV with dialog for format and range selection
• Fullscreen Mode (F key / F11) - enter fullscreen on active visualization tab, exit button overlay
• Connection Status Widget - persistent indicator in header showing WebSocket/sensing connection state (connected/reconnecting/offline) with reconnect button

All features are accessible via keyboard shortcuts and the command palette. New shortcuts: L (activity log), E (export), F (fullscreen).

Test plan

• Press Ctrl+K to open command palette, type "demo" to filter, press Enter to navigate
• Press L to toggle activity log, verify console messages appear in real-time
• Use filter buttons (I/W/E/C) to toggle message types, press Clear
• Press E to open export dialog (needs sensor data; verify warning toast if no data)
• Press F or F11 to enter fullscreen on active tab, verify exit button appears
• Verify connection status widget in header shows correct state
• Click reconnect button when disconnected
• Test on mobile viewport (connection label hides, palette adapts)