feat(sieve): local email filters alongside server filters (#90)

Reuse the same Sieve UI for both server-side (ManageSieve/JMAP) and local
email filters. Both filter sets are stored and managed independently.

Changes:
- Add LocalSieveScripts table (DB schema v29) to store local Sieve scripts
- Add LocalSieveRepository with full CRUD and activate-script support
- Add isLocal param to SieveScriptsScreen and SieveScriptEditScreen; each
  screen shows a banner explaining whether scripts run on the server or device
- Add routes /accounts/:id/sieve/local and /accounts/:id/sieve/local/edit
- Split "Email filters" account menu entry into "Server email filters" and
  "Local email filters" (local is always available, server requires ManageSieve)
- Wire up localSieveRepositoryProvider in DI

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

lib/data/db/database.dart

@@ -243,6 +243,16 @@ class SearchHistoryEntries extends Table {
   DateTimeColumn get searchedAt => dateTime()();
 }
 
+@DataClassName('LocalSieveScriptRow')
+class LocalSieveScripts extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get accountId =>
+      text().references(Accounts, #id, onDelete: KeyAction.cascade)();
+  TextColumn get name => text()();
+  TextColumn get content => text().withDefault(const Constant(''))();
+  BoolColumn get isActive => boolean().withDefault(const Constant(false))();
+}
+
 @DataClassName('UndoActionRow')
 class UndoActions extends Table {
   TextColumn get id => text()();
@@ -273,13 +283,14 @@ class UndoActions extends Table {
     SyncHealth,
     UndoActions,
     SearchHistoryEntries,
+    LocalSieveScripts,
   ],
 )
 class AppDatabase extends _$AppDatabase {
   AppDatabase([QueryExecutor? executor]) : super(executor ?? _openConnection());
 
   @override
-  int get schemaVersion => 28;
+  int get schemaVersion => 29;
 
   Future<void> _createEmailFts() async {
     await customStatement('''
@@ -508,6 +519,9 @@ class AppDatabase extends _$AppDatabase {
           if (from < 28) {
             await m.addColumn(emailBodies, emailBodies.mimeTreeJson);
           }
+          if (from < 29) {
+            await m.createTable(localSieveScripts);
+          }
         },
       );
 }

lib/data/db/local_sieve_repository.dart

@@ -0,0 +1,101 @@
+import 'package:drift/drift.dart';
+
+import 'package:sharedinbox/core/models/sieve_script.dart';
+import 'package:sharedinbox/data/db/database.dart';
+
+class LocalSieveRepository {
+  LocalSieveRepository(this._db);
+
+  final AppDatabase _db;
+
+  Future<List<SieveScript>> listScripts(String accountId) async {
+    final rows = await (_db.select(_db.localSieveScripts)
+          ..where((t) => t.accountId.equals(accountId)))
+        .get();
+    return rows
+        .map(
+          (r) => SieveScript(
+            id: r.id.toString(),
+            name: r.name,
+            blobId: r.id.toString(),
+            isActive: r.isActive,
+          ),
+        )
+        .toList();
+  }
+
+  Future<String> getScriptContent(String accountId, String blobId) async {
+    final rowId = int.parse(blobId);
+    final row = await (_db.select(_db.localSieveScripts)
+          ..where(
+            (t) => t.id.equals(rowId) & t.accountId.equals(accountId),
+          ))
+        .getSingleOrNull();
+    if (row == null) throw Exception('Local script not found: $blobId');
+    return row.content;
+  }
+
+  Future<SieveScript> saveScript(
+    String accountId, {
+    String? id,
+    required String name,
+    required String content,
+  }) async {
+    if (id != null) {
+      final rowId = int.parse(id);
+      await (_db.update(_db.localSieveScripts)
+            ..where(
+              (t) => t.id.equals(rowId) & t.accountId.equals(accountId),
+            ))
+          .write(
+        LocalSieveScriptsCompanion(
+          name: Value(name),
+          content: Value(content),
+        ),
+      );
+      final updated = await (_db.select(_db.localSieveScripts)
+            ..where(
+              (t) => t.id.equals(rowId) & t.accountId.equals(accountId),
+            ))
+          .getSingleOrNull();
+      return SieveScript(
+        id: id,
+        name: name,
+        blobId: id,
+        isActive: updated?.isActive ?? false,
+      );
+    }
+    final rowId = await _db.into(_db.localSieveScripts).insert(
+          LocalSieveScriptsCompanion.insert(
+            accountId: accountId,
+            name: name,
+            content: Value(content),
+          ),
+        );
+    final idStr = rowId.toString();
+    return SieveScript(id: idStr, name: name, blobId: idStr, isActive: false);
+  }
+
+  Future<void> deleteScript(String accountId, String scriptId) async {
+    final rowId = int.parse(scriptId);
+    await (_db.delete(_db.localSieveScripts)
+          ..where(
+            (t) => t.id.equals(rowId) & t.accountId.equals(accountId),
+          ))
+        .go();
+  }
+
+  Future<void> activateScript(String accountId, String scriptId) async {
+    await _db.transaction(() async {
+      await (_db.update(_db.localSieveScripts)
+            ..where((t) => t.accountId.equals(accountId)))
+          .write(const LocalSieveScriptsCompanion(isActive: Value(false)));
+      final rowId = int.parse(scriptId);
+      await (_db.update(_db.localSieveScripts)
+            ..where(
+              (t) => t.id.equals(rowId) & t.accountId.equals(accountId),
+            ))
+          .write(const LocalSieveScriptsCompanion(isActive: Value(true)));
+    });
+  }
+}