fix: use permission_handler for battery optimization checks

[zlshames]

Replaces the forked disable_battery_optimization plugin with permission_handler's Permission.ignoreBatteryOptimizations, which was already a dependency and calls the same PowerManager.isIgnoringBatteryOptimizations() / ACTION_REQUEST_IGNORE_BATTERY_OPTIMIZATIONS under the hood.

Split out of the Android build work so the Gradle/AGP upgrade can be reviewed separately.

Why

The plugin was 2,633 lines of Java across 26 files; the app used two methods. The rest is OEM autostart handling reachable only through methods we never call.

The part we did use was wrong. isAllBatteryOptimizationDisabled ANDed the real OS check with two SharedPreferences flags that cached !KillerManager.isActionAvailable(...) on first read and were only ever set by dialog flows the app never invoked. On any device whose OEM ships an autostart settings screen — Samsung, Xiaomi, Oppo, Huawei — that cached false permanently, so the check reported "not disabled" even after the user granted the exemption. Those are exactly the manufacturers whose battery management makes the check matter.

Changes

• Manifest: declares REQUEST_IGNORE_BATTERY_OPTIMIZATIONS directly. It used to arrive via the plugin's manifest merger, and permission_handler_android ships an empty manifest by design — without this the permission silently disappears and request() never opens the system prompt. Also drops the plugin's stray oppo.permission.OPPO_COMPONENT_SAFE.
• Jetifier off: the plugin's material-dialogs:0.9.6.0 pulled com.android.support and was the only thing keeping android.enableJetifier on. With it gone, ./gradlew checkJetifier reports 57/57 projects clean. AGP 9.1+ rejects the flag outright, so this had to happen regardless.
• Live status: both surfaces re-read on AppLifecycleState.resumed. The exemption is granted in a system dialog, so returning to the foreground is the only signal it changed; the setup page previously checked once and never updated.
• Setup page now shows status in both states — it rendered nothing at all when optimizations were still enabled.
• Developer Tools tile routes to openAppSettings() when already exempt. Android has no revoke API, so undoing this has to be a trip to system settings rather than the "Already Disabled" dead end it was.

Testing

Verified on an Android 16 (API 36) emulator, prod flavor:

• Setup page correctly shows red "Enabled" + button when not exempt
• Tapping through launches the real com.android.settings/.fuelgauge.RequestIgnoreBatteryOptimizations dialog
• Allow adds the app to the deviceidle whitelist and the page flips to a green check with no restart
• Revoking via adb and relaunching shows the "Enabled" state again
• Debug + release APKs build; app launches with no NoClassDefFoundError

Not verified: the Developer Tools tile itself — it sits behind a configured server I don't have. It shares the same helpers as the setup page, which are verified, but the tile UI is untested.

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