feat: switch folder-view search from IMAP to local SQLite FTS5

Closes #501

searchEmails now queries the local email_fts virtual table filtered by
mailbox_path instead of doing a live IMAP SEARCH. This makes folder-view
search work offline and ensures tapped results always open the correct
email (IDs come from the same local DB that getEmail reads from).

Reuses the existing FTS5 infrastructure (_toFtsQuery + the email_fts
content-table join) from searchEmailsGlobal, adding only the
`AND e.mailbox_path = ?` filter.

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

lib/data/repositories/email_repository_impl.dart

@@ -3052,63 +3052,26 @@ class EmailRepositoryImpl implements EmailRepository {
     String mailboxPath,
     String query,
   ) async {
-    final account = (await _accounts.getAccount(accountId))!;
-    final password = await _accounts.getPassword(accountId);
-    final client = await _imapConnect(
-      account,
-      _effectiveUsername(account),
-      password,
+    final ftsQuery = _toFtsQuery(query);
+    if (ftsQuery.isEmpty) return [];
+
+    const sql = 'SELECT e.* FROM email_fts f JOIN emails e ON e.rowid = f.rowid'
+        ' WHERE email_fts MATCH ? AND e.account_id = ? AND e.mailbox_path = ?'
+        ' ORDER BY rank LIMIT 50';
+    final variables = [
+      Variable<String>(ftsQuery),
+      Variable<String>(accountId),
+      Variable<String>(mailboxPath),
+    ];
+
+    final queryRows = await _db
+        .customSelect(sql, variables: variables, readsFrom: {_db.emails}).get();
+    final emailRows = await Future.wait(
+      queryRows.map((r) => _db.emails.mapFromRow(r)),
     );
-    try {
-      await client.selectMailboxByPath(mailboxPath);
-      final terms =
-          query.split(RegExp(r'\s+')).where((t) => t.isNotEmpty).toList();
-      final searchCriteria = terms.map((term) {
-        final escaped = term.replaceAll('"', '\\"');
-        return 'OR SUBJECT "$escaped" TEXT "$escaped"';
-      }).join(' ');
-      final result = await client.uidSearchMessages(
-        searchCriteria: searchCriteria,
-      );
-      final uids = result.matchingSequence?.toList() ?? [];
-      if (uids.isEmpty) return [];
-
-      final fetch = await client.uidFetchMessages(
-        imap.MessageSequence.fromIds(uids, isUid: true),
-        '(UID FLAGS ENVELOPE)',
-      );
-      return fetch.messages
-          .where((msg) => msg.uid != null && msg.envelope != null)
-          .map((msg) {
-        final envelope = msg.envelope!;
-        final uid = msg.uid!;
-        final emailId = '$accountId:$uid';
-        return model.Email(
-          id: emailId,
-          accountId: accountId,
-          mailboxPath: mailboxPath,
-          uid: uid,
-          subject: envelope.subject,
-          sentAt: envelope.date,
-          receivedAt: envelope.date ?? DateTime.now(),
-          from: _toAddressList(envelope.from),
-          to: _toAddressList(envelope.to),
-          cc: _toAddressList(envelope.cc),
-          isSeen: msg.flags?.contains(r'\Seen') ?? false,
-          isFlagged: msg.flags?.contains(r'\Flagged') ?? false,
-          hasAttachment: msg.hasAttachments(),
-        );
-      }).toList();
-    } finally {
-      await client.logout();
-    }
+    return emailRows.map(_toModel).toList();
   }
 
-  List<model.EmailAddress> _toAddressList(List<imap.MailAddress>? addresses) =>
-      (addresses ?? const [])
-          .map((a) => model.EmailAddress(name: a.personalName, email: a.email))
-          .toList();
-
   // ── Helpers ────────────────────────────────────────────────────────────────
 
   /// Computes a stable threadId from RFC 2822 headers.