Add screensaver coordination and local fallback handling

[loopy321]

Summary

This PR updates the VACA Home Assistant integration to coordinate correctly with the companion app screensaver/navigation changes.

It adds the integration-side handling needed for idle-driven dashboard screensaver behavior, preserves the original local screen-off fallback when no screensaver dashboard path is configured, and keeps settings propagation aligned with the app.

Included changes

• Add integration-side handling for ui_idle-driven screensaver navigation
• Only trigger dashboard screensaver when the current path is the default home path
• Preserve local screen-off fallback when no screensaver dashboard path is configured
• Reset stale idle state on reconnect
• Allow blank screensaver dashboard path values
• Update screensaver-related settings propagation so partial updates do not disable the wrong behavior

Validation

Validated with the companion app on the Lenovo tablet:

• idle transitions trigger dashboard screensaver when configured
• blank screensaver dashboard path restores original local screen-off behavior
• reconnects do not leave stale idle state behind
• settings updates continue to behave correctly with the app-side flow

Related changes

This PR is one part of a coordinated update across the companion app and Home Assistant integrations.

Related PRs:

• App: Add HA screensaver flow, auth hardening, and tablet recovery fixes ViewAssistCompanionApp#27
• view_assist integration: Forward tablet navigate/revert actions for VACA devices view_assist_integration#4

Recommended rollout: merge and deploy the related PRs together.

[loopy321]

Follow-up: this branch now adds a restart-ui custom action/button for the Android-10 Lenovo tablet.

Why it was needed:

• the Android-10 Lenovo tablet could reach a black-screen zombie state where normal screen-wake and refresh actions were too weak to recover the visible UI
• testing showed that a real app/UI restart reliably restored rendering
• this new action exposes that recovery path through Home Assistant, so automations can recover the device without adb