Fix screen-lock background tracking reliability

[sohamvjadhav]

What changed

• Keep the service watchdog alive when location initialization fails.
• Re-register GPS updates after screen lock/Doze when callbacks become stale.
• Re-check location permission during watchdog recovery.
• Persist the user-enabled service intent across sticky service restarts while respecting an explicit Stop.
• Move the battery-optimization prompt until after service launch.
• Surface failed service starts instead of silently appearing idle.
• Reset speed-filter history when switching between GPS and motion sources.
• Add focused unit tests for filtering and motion fallback.

Root cause

The watchdog returned permanently when the location manager was unavailable, and it did not recover requests that remained registered but stopped delivering callbacks after lock/Doze. The start path also opened Settings before launching the foreground service, which made some OEMs treat the launch as background-originated.

Validation

• ./gradlew testDebugUnitTest passed
• ./gradlew lintDebug passed with advisory warnings only
• ./gradlew assembleDebug passed
• git diff --check passed

Physical locked-screen and OEM battery-policy testing is still required before merging.