Merge remote-tracking branch 'origin/main' into feat-screen-unlock

Brings the screen-lock app gate (#22) up to date with 25 commits of main
(signatures, backup opt-in, battery optimization, rich compose, reporting).

Conflicts resolved as a union of both features:
- SettingsRepository: adopt main's top-level Keys + shared toAppSettings()
  refactor and thread appLock through it; keep both appLock and includeInBackup
- DatabaseModule: keep provideSignatureDao; keep DatabaseFiles.NAME for DB_NAME
- MainActivity: wrap LibreMailApp(pendingCompose=...) inside AppLockGateHost
- SettingsViewModel/SettingsScreen: union app-lock and battery state/effects;
  keep LocalResources for the app-lock toast (LocalContextGetResourceValueCall lint)
- SettingsScreenTest: construct SettingsViewModel with the merged 5 args
- strings.xml: keep both the app-lock and battery/diagnostics string blocks

Fast gate green with JDK 21: assembleDebug + testDebugUnitTest + lintDebug +
compileDebugAndroidTestKotlin.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

gradle/libs.versions.toml

@@ -89,6 +89,7 @@ mockk = { group = "io.mockk", name = "mockk", version.ref = "mockk" }
 greenmail = { group = "com.icegreen", name = "greenmail", version.ref = "greenmail" }
 androidx-junit = { group = "androidx.test.ext", name = "junit", version.ref = "androidxJunit" }
 androidx-espresso-core = { group = "androidx.test.espresso", name = "espresso-core", version.ref = "espresso" }
+androidx-espresso-intents = { group = "androidx.test.espresso", name = "espresso-intents", version.ref = "espresso" }
 
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }