Fix overlay flicker and removal race conditions

[kasnder]

Summary

Addresses two reported overlay artifacts: (1) overlays briefly disappearing and reappearing while still in the target app, and (2) overlays staying visible after leaving the app.

Flicker — onAccessibilityEvent is too eager to clear

• Only TYPE_WINDOW_STATE_CHANGED from a foreign package now counts as a leave signal. Content changes and scrolls from systemui (e.g. status bar updates from an arriving notification) or the launcher no longer trigger a clear while the target app is still the active window underneath.
• Foreign window-state changes are debounced by 150ms; any subsequent event from the target package cancels the pending clear. This absorbs transient focus changes such as a briefly pulled notification shade.

Race — OverlayManager add/remove was partly async, partly sync

• All OverlayManager operations are now synchronous on the caller's thread (always main for the accessibility service). A queued addView can no longer run after a clear and leave an orphan view attached but untracked.
• clearOverlays can no longer empty the tracker list before removeView has actually detached the views.
• forceClearAllOverlays collapses to a clearAllOverlays alias since both paths are now equivalent.

Cleanup

• Pending clear runnable is cancelled in all teardown paths (reloadRulesFromSource, reevaluateBlockingState, screen off, onInterrupt, onDestroy).

Considered and rejected

• Per-element grace period (e.g. keep an overlay alive 500ms past its node's last appearance): would pin overlays at stale positions while a feed scrolls beneath them (Instagram-style), which is a worse artifact than a brief flicker.
• Widening info.packageNames = null to receive events for unmonitored apps: would fix the case where a switch never delivers an event to the service, but increases battery cost on every other app.

Test plan

• Open WhatsApp with a rule active; pull and release the notification shade quickly. Overlay should not disappear.
• Open WhatsApp with a rule active; let a notification arrive without pulling the shade. Overlay should not flicker.
• Scroll the Instagram feed (or similar) with a rule active. Overlays should follow scrolled elements without sticking at stale positions.
• Switch from a rule app to launcher. Overlays should clear within ~150ms.
• Switch from a rule app to another rule app. Overlays for the first should clear, the second's should appear.
• Lock screen, then unlock and return to the rule app. Overlays should re-evaluate correctly.

https://claude.ai/code/session_018ChatjS8SFHCh8w7ySjCte