Fix: Prevent crash when app is launched during automatic backup

[d4rken]

What changed

Fixed a crash that could happen when SD Maid was launched while Android's automatic backup was running. On Android 13 and below, this crash could also break subsequent app launches until the device was restarted.

Developer TLDR

• Removed @AndroidEntryPoint from all 4 BroadcastReceivers (SchedulerRestoreReceiver, UnarchiveReceiver, UninstallWatcherReceiver, ExternalWatcherTaskReceiver)
• Hilt's bytecode transformation injects super.onReceive() before any user code, making it impossible to guard with @AndroidEntryPoint. Switched to manual EntryPointAccessors.fromApplication() per Dagger team recommendation
• Added Context.isValidHiltContext() helper in InjectionHelpers.kt and consolidated existing Service.isValidAndroidEntryPoint() to delegate to it
• Each receiver validates intent/extras before DI lookup (cheap checks first), with try-catch defense-in-depth around EntryPointAccessors
• Dropped unused CorpseFinderSettings injection from ExternalWatcherTaskReceiver
• Added BroadcastReceiverBackupGuardTest regression test verifying all 4 receivers silently return with a restricted context

Background & research

Root cause

When Android Auto Backup runs, it invokes registered BroadcastReceivers with a RestrictedContext whose applicationContext is a plain android.app.Application — not our @HiltAndroidApp App. Hilt's Gradle plugin performs bytecode transformation on @AndroidEntryPoint receivers, inserting a super.onReceive() call at the very beginning of onReceive() — before any user code. This makes it impossible to add a guard check while using @AndroidEntryPoint.

On Android <= 13, there's a platform bug (Google issue #160946170) where crashing during backup causes the "restricted" flag to persist, breaking subsequent app launches until the device is restarted.

Why EntryPointAccessors instead of alternatives

Approach	Verdict
Keep @AndroidEntryPoint + add guard in onReceive	Not possible — Hilt bytecode transformation injects super.onReceive() before our code
android:allowBackup="false"	Works but users lose backup/restore entirely
Custom BackupAgent	Significant extra work, doesn't prevent the receiver from being invoked
Remove @AndroidEntryPoint + manual EntryPointAccessors	Dagger team's recommended approach (#2798)

Known tradeoff

With @AndroidEntryPoint, adding a dependency was just @Inject lateinit var foo: Foo. Now someone needs to also add the method to the ReceiverEntryPoint interface and call it manually. Forgetting the interface method is a compile error (Dagger can't find the binding), so it's not silent — just more friction.

Related issues

• Dagger #2798: Provide warning about using "allowBackup" with Hilt — Dagger team acknowledged but only proposed documentation changes, no code-level fix
• Google #160946170: Restricted mode persists after backup crash — Android platform bug, no public fix
• Dagger #1918: Hilt injection not working in BroadcastReceiver — related general discussion

Closes #1274