Recover from corrupted secure auth storage

[Komzpa]

Summary

• treat unreadable or non-JSON secure auth tokens as logged-out state and clear secure storage so OAuth can start fresh
• add an Android native fallback that clears only Flutter secure-storage shared preferences when the plugin cannot initialize/delete them itself
• exclude Flutter secure-storage data/key/config shared-pref files from legacy backup and Android 12+ cloud/device-transfer rules
• add a regression test for the secure-storage recovery marker and malformed stored tokens

Fixes #951.
Fixes #1001.
Fixes #1030.

Evidence

On a migrated Samsung SM-F766B / Android 16 device running Every Door 7.1.0, launching the app logs:

SecureStorageAndroid: EncryptedSharedPreferences initialization failed
javax.crypto.AEADBadTagException
Caused by: android.security.KeyStoreException: Signature/MAC verification failed

That failure happens before normal OAuth token parsing can recover, so the PR now has a native shared-preferences cleanup fallback that does not clear the app database or unsent edits.

Testing

• git diff --check HEAD~1..HEAD
• xmllint --noout android/app/src/main/res/xml/backup_rules.xml android/app/src/main/res/xml/data_extraction_rules.xml android/app/src/main/AndroidManifest.xml
• ADB logcat on the affected device confirms the secure-storage MAC verification failure above

Not run: flutter test / flutter analyze; this machine does not have Flutter or Dart installed.