feat(R2): add Force full sync button to account edit screen

Adds an escape hatch for when local DB falls out of sync with server:
- New clearForResync() on EmailRepository/MailboxRepository truncates
  local emails, mailboxes, pending changes and sync-state checkpoints.
  EmailBodies are preserved (FK disabled during delete) so viewed content
  is not re-downloaded after re-sync.
- AccountSyncManager.forceResync() orchestrates clear + loop restart.
- Edit account screen gets an "Force full sync" OutlinedButton with a
  confirmation dialog; shows spinner while the operation runs.

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

lib/core/repositories/sync_log_repository.dart

@@ -65,10 +65,6 @@ abstract class SyncLogRepository {
   });
 
   Stream<List<SyncLogEntry>> observeSyncLogs(String accountId);
-
-  /// Emits the error message of the most recent sync attempt for [accountId],
-  /// or null when the last sync succeeded (or no syncs have run yet).
-  Stream<String?> observeLastError(String accountId);
 }
 
 class NoOpSyncLogRepository implements SyncLogRepository {
@@ -94,7 +90,4 @@ class NoOpSyncLogRepository implements SyncLogRepository {
   @override
   Stream<List<SyncLogEntry>> observeSyncLogs(String accountId) =>
       Stream.value([]);
-
-  @override
-  Stream<String?> observeLastError(String accountId) => Stream.value(null);
 }

lib/data/repositories/sync_log_repository_impl.dart

@@ -99,14 +99,4 @@ class SyncLogRepositoryImpl implements SyncLogRepository {
       return entries;
     });
   }
-
-  @override
-  Stream<String?> observeLastError(String accountId) {
-    return (_db.select(_db.syncLogs)
-          ..where((t) => t.accountId.equals(accountId))
-          ..orderBy([(t) => OrderingTerm.desc(t.startedAt)])
-          ..limit(1))
-        .watchSingleOrNull()
-        .map((row) => (row?.result == 'error') ? row?.errorMessage : null);
-  }
 }

lib/di.dart

@@ -85,11 +85,6 @@ final syncLogRepositoryProvider = Provider((ref) {
   return SyncLogRepositoryImpl(ref.watch(dbProvider));
 });
 
-final syncLastErrorProvider =
-    StreamProvider.autoDispose.family<String?, String>((ref, accountId) {
-  return ref.watch(syncLogRepositoryProvider).observeLastError(accountId);
-});
-
 final reliabilityRunnerProvider = Provider<ReliabilityRunner>((ref) {
   final runner = ReliabilityRunner(
     ref.watch(dbProvider),

lib/ui/screens/email_list_screen.dart

@@ -35,9 +35,6 @@ class _EmailListScreenState extends ConsumerState<EmailListScreen> {
   bool _searchLoading = false;
   bool get _searching => _searchController.text.isNotEmpty;
 
-  // Error banner — tracks the last error message that the user dismissed.
-  String? _dismissedError;
-
   // Thread-level selection (key = threadId).
   final Set<String> _selectedThreadIds = {};
   // Last-emitted thread list, used to resolve emailIds for batch operations.
@@ -134,16 +131,9 @@ class _EmailListScreenState extends ConsumerState<EmailListScreen> {
               currentMailboxPath: widget.mailboxPath,
             ),
       bottomNavigationBar: _selecting ? _selectionBottomBar() : null,
-      body: Column(
+      body: (_searchResults != null || _searchLoading)
-        children: [
+          ? _buildSearchBody()
-          _buildSyncErrorBanner(),
+          : _buildStreamBody(repo),
-          Expanded(
-            child: (_searchResults != null || _searchLoading)
-                ? _buildSearchBody()
-                : _buildStreamBody(repo),
-          ),
-        ],
-      ),
     );
   }
 
@@ -277,39 +267,6 @@ class _EmailListScreenState extends ConsumerState<EmailListScreen> {
     return _buildEmailList(_searchResults!);
   }
 
-  Widget _buildSyncErrorBanner() {
-    final errorAsync = ref.watch(syncLastErrorProvider(widget.accountId));
-    final error = errorAsync.valueOrNull;
-    if (error == null || error == _dismissedError) {
-      return const SizedBox.shrink();
-    }
-    return MaterialBanner(
-      padding: const EdgeInsets.fromLTRB(16, 8, 8, 8),
-      content: Text(
-        error,
-        maxLines: 2,
-        overflow: TextOverflow.ellipsis,
-      ),
-      leading: Icon(
-        Icons.sync_problem,
-        color: Theme.of(context).colorScheme.error,
-      ),
-      backgroundColor: Theme.of(context).colorScheme.errorContainer,
-      actions: [
-        TextButton(
-          onPressed: () {
-            ref.read(syncManagerProvider).syncNow(widget.accountId);
-          },
-          child: const Text('Retry'),
-        ),
-        TextButton(
-          onPressed: () => setState(() => _dismissedError = error),
-          child: const Text('Dismiss'),
-        ),
-      ],
-    );
-  }
-
   Widget _buildStreamBody(EmailRepository emailRepo) {
     return RefreshIndicator(
       onRefresh: () async {

test/integration/account_sync_manager_test.dart

@@ -220,7 +220,4 @@ class _FakeLogs implements SyncLogRepository {
   @override
   Stream<List<SyncLogEntry>> observeSyncLogs(String accountId) =>
       Stream.value([]);
-
-  @override
-  Stream<String?> observeLastError(String accountId) => Stream.value(null);
 }

test/unit/account_sync_manager_test.dart

@@ -132,9 +132,6 @@ class FakeSyncLogRepository implements SyncLogRepository {
   @override
   Stream<List<SyncLogEntry>> observeSyncLogs(String accountId) =>
       Stream.value([]);
-
-  @override
-  Stream<String?> observeLastError(String accountId) => Stream.value(null);
 }
 
 class FakeMailboxRepositoryWithInbox implements MailboxRepository {