Adds a close button and session-scoped dismissal flag so the banner
can be acknowledged for the current run but reappears on the next
app launch if the fallback is still active — matches the #81
acceptance criterion.
- sessionStorage key survives page navigation within the run, is
cleared on app restart.
- Graceful on storage quota errors.
- New `common.close` i18n key (FR: "Fermer", EN: "Close") used as
the aria-label of the close button.
Adds a visible warning in the Settings page when `token_store` has
landed in the file fallback instead of the OS keychain. Without this,
a user on a keychain-less system would silently lose the security
benefit introduced in #78 and never know.
- New `get_token_store_mode` service wrapper in authService.ts.
- New `TokenStoreFallbackBanner` component: fetches the mode on mount,
renders nothing when mode is `keychain` or null, renders an
amber warning card when mode is `file`.
- Mounted in SettingsPage right after AccountCard so it sits next to
the account state the user can fix (log out + log back in once the
keychain is available).
- i18n keys under `account.tokenStore.fallback.*` in fr/en.
Refs #66
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
