Arm scanning automatically whenever the switches allow it

[enaboapps]

Scanning no longer has an enable button. It is armed whenever the saved switches cover the current mode and the environment allows it, and it stays that way while Switchify runs.

Behaviour

• The runtime reconciles on every tick while scanning is off: it arms when a Select switch exists (plus Next and Previous in manual mode), no key is being learned, Android is not connected, and input access is granted. A failed key reservation backs off two seconds between attempts.
• Saving switches and starting key learning pause scanning instead of being refused while it runs. The Switches tab is never locked, and changes to scan settings apply straight away.
• Escape and the emergency hold reset the scan; the keys are re-reserved on the next tick. Nothing waits for window focus.
• Scanning arms at launch, so assigned keys are reserved from startup. Application exit halts the reconciler before shutting the input broker.
• The Scanning tab shows the backend's message as its status line: ready, the reason scanning is off, or the current phase.

IPC

configure_point_scan drops its enabled argument. get_point_scan, the point-scan-changed event and point-scan.json keep their shapes. save_switches and begin_switch_capture no longer fail when scanning is on.

Validation

tsc, 131 frontend tests plus 5 Node tests, cargo fmt, Clippy all targets with warnings denied, 304 Rust unit tests and 7 integration tests passed on Windows. Tests use fake input and do not send desktop input.

Live check against the dev build with a real saved Space switch: scanning was armed at launch; saving a probe switch re-armed it; changing line speed while armed re-armed it; saving an empty switch list disarmed it with "Scanning starts once a switch has the Select action"; restoring the switch re-armed it. No key events were sent by the agent.

Manual checks remaining: Escape followed by re-arm on a physical switch, learning a key while scanning is armed, an Android connection ending, and a key held by another application while Switchify starts.

Builds on #731.

[greptile-apps]

Greptile Summary

The PR replaces the manual point-scan toggle with automatic scanning lifecycle reconciliation. It arms scanning when switch assignments and environment checks permit it, pauses safely during configuration and input-handling transitions, and re-arms when scanning becomes eligible again.

Confidence Score: 5/5

Safe to merge.

The previously reported retry-delay issue is resolved: environmental readiness failures return before retry timing is considered, while the retry delay remains limited to arm failures. enaboapps manually resolved the earlier thread without explanation.

_{Reviews (2): Last reviewed commit: "Re-check the environment every tick inst..." | Re-trigger Greptile}