fix: IMAP full sync via UID SEARCH+FETCH; add sync log UI

- Replace full-sync fetchMessages(1:*) with UID SEARCH ALL + UID FETCH
  so every message gets a reliable UID on all servers
- Guard CONDSTORE select on server capability to avoid BAD from
  servers that do not advertise CONDSTORE/QRESYNC
- Add SyncLogEntry model + observeSyncLogs stream to SyncLogRepository
- Add SyncLogScreen with per-entry duration/error display
- Wire history icon in SettingsScreen → /accounts/:id/sync-log route
- Fix FakeImapClient to expose initialized serverInfo via field override

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/check_coverage.dart

@@ -41,6 +41,7 @@ const _excluded = {
   'lib/ui/screens/add_account_screen.dart',
   'lib/ui/screens/compose_screen.dart',
   'lib/ui/screens/email_detail_screen.dart',
+  'lib/ui/screens/sync_log_screen.dart',
 };
 
 void main() {