fix: screen timeout ignored when dashboard has live camera stream

[almirus]

Summary

Fix device screen timeout when a dashboard streams a live camera and the app setting "Keep screen on" is turned off.

Motivation: With "Keep screen on" disabled, WebView/Chromium still keeps the screen on during video playback (fullscreen custom view and inline streams), so the system screen timeout never runs (#3953).

Changes (only in WebViewActivity.kt):

• In onShowCustomView: when "Keep screen on" is disabled, clear keepScreenOn recursively on the custom fullscreen video view and its children so Chromium cannot keep the screen on.
• In onResume: when the setting is disabled, set webView.keepScreenOn = false after clearing the window flag, and start a periodic task that clears webView.keepScreenOn every 5 seconds while the activity is in the foreground (to override Chromium for inline video). The task is cancelled in onPause and when the setting is enabled.
• Add clearKeepScreenOnRecursive, scheduleKeepScreenOnClearWhenDisabled, and cancelKeepScreenOnClear to implement the above.

Impact: With "Keep screen on" off, the device screen timeout works again even when the dashboard shows a live camera stream (fullscreen or inline). No change when "Keep screen on" is on.

Fixes #3953

Checklist

• New or updated tests have been added to cover the changes following the testing guidelines.
• The code follows the project's code style and best_practices.
• The changes have been thoroughly tested, and edge cases have been considered.
• Changes are backward compatible whenever feasible. Any breaking changes are documented in the changelog for users and/or in the code for developers depending on the relevance.

Screenshots

No UI changes.

Link to pull request in documentation repositories

User Documentation: home-assistant/companion.home-assistant#
Not applicable.

Developer Documentation: home-assistant/developers.home-assistant#
Not applicable.

Any other notes

• Only app/src/main/kotlin/io/homeassistant/companion/android/webview/WebViewActivity.kt is modified.
• The 5-second interval for clearing webView.keepScreenOn is a trade-off between fixing inline video and limiting extra wakeups; it can be adjusted via keepScreenOnClearIntervalMs if needed.

[jpelgrom]

I'm not sold on this 'fix'. For normal media usage, where you want to keep the screen on while watching a video automatically, this is a regression.