Scope keyboard controls to open trays

[ridecontrol]

What changed

• Give the Sessions tray its own chart-selection state instead of sharing the dashboard preference.
• Route Left/Right chart navigation to the selected session while the tray is open.
• Preserve Up/Down saved-session navigation and keep dashboard controls inactive behind overlays.

Root cause

The dashboard and saved-session charts both wrote to one persisted chart mode. The dashboard keyboard listener was disabled correctly, but changing the tray chart still updated that shared state and visibly changed the dashboard behind it.

Impact

Keyboard controls now affect only the open tray. Closing the tray reveals the dashboard with its prior chart selection unchanged.

Validation

• bun run ci
• 257 tests passed
• Biome completed with warnings treated as errors
• Tailwind diagnostics passed
• TypeScript passed
• Production Vite build passed