fix: #228 #229 #230 #231 OTP accessibility, notification prefs, 2FA backgrounding tests, TOTP clipboard auto-clear

[Young850]

#230 - Add VoiceOver/TalkBack accessibility labels to OTP field (iOS + Android)
iOS: .accessibilityLabel/.accessibilityValue/.accessibilityHint on TextField
Android: semantics { contentDescription } on OutlinedTextField
docs: new OTP accessibility section in manual-qa-checklist.md

#231 - Add NotificationPreferencesView/Screen (iOS + Android)
iOS: NotificationPreferences model + NotificationPreferencesView, wired into SettingsView
Android: NotificationPreferences model + NotificationPreferencesViewModel +
NotificationPreferencesScreen, wired into MainActivity NavHost
Both platforms sync preferences server-side (POST /notifications/preferences)

#229 - Add 2FA backgrounding tests (iOS + Android)
iOS: TwoFactorBackgroundingTests.swift (OTPRateLimiter + AuthStore scene-phase tests)
Android: TwoFactorBackgroundingTest.kt (ViewModel state preservation across process death)
Assert OTP digits cleared on resume, cooldown persists, no stale isLoading

#228 - Add TOTP secret clipboard auto-clear + one-time warning (iOS + Android)
iOS: TOTPSecretCopyView with 30s auto-clear and UserDefaults-backed one-time alert
Android: TotpSecretCopyRow with coroutine-based 30s auto-clear and SharedPrefs warning
Tests: TOTPClipboardTests.swift + TotpClipboardTest.kt

Update .gitignore: exclude snapshot images, build artifacts, IDE files

Summary

Changes

Testing

Parity checklist

This project maintains a feature-parity table in PARITY.md that
tracks which features are implemented on iOS vs Android. Please answer the
questions below before requesting review.

• This PR does not add, change, or remove any user-facing feature on either
  platform — no PARITY.md update needed.

  — OR —

• This PR adds/changes/removes a user-facing feature. I have updated PARITY.md:

  • Updated the status symbol(s) for the affected row(s).
  • Added or updated "Notes" if the implementation is partial or has caveats.
  • Removed or updated any rows in the "Known gaps" table that this PR closes.

Related issues

Closes #228
Closes #229
Closes #230
Closes #231

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