FB-05: closed-loop routes in Route Planner

Add an isClosedLoop toggle to route plans (schema v3 -> v4 migration),
threaded through the domain model, repository distance recomputation,
the overflow menu, and the drawn polyline, so a route can loop back to
its first waypoint.

test/migration_test.dart

@@ -177,4 +177,57 @@ void main() {
     final waypoints = await db.waypointsForRoute(routeId);
     expect(waypoints, hasLength(1));
   });
+
+  test('a v3 database (FB-05) gains isClosedLoop defaulting to false', () async {
+    // v3: identical to the v2 seed above, plus the route_plans/waypoints tables V3-07
+    // added.
+    seedV1Database();
+    final raw = sqlite3.sqlite3.open(dbFile.path);
+    raw.execute('''
+      ALTER TABLE trips ADD COLUMN activity TEXT NOT NULL DEFAULT 'motorcycle';
+    ''');
+    raw.execute('''
+      CREATE TABLE route_plans (
+        id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
+        name TEXT NOT NULL,
+        createdAt INTEGER NOT NULL,
+        activity TEXT NOT NULL DEFAULT 'motorcycle',
+        distanceM REAL NOT NULL DEFAULT 0,
+        estimatedMillis INTEGER NULL,
+        geometry TEXT NULL
+      );
+      CREATE TABLE waypoints (
+        id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
+        routeId INTEGER NOT NULL REFERENCES route_plans (id) ON DELETE CASCADE,
+        ordinal INTEGER NOT NULL,
+        latitude REAL NOT NULL,
+        longitude REAL NOT NULL,
+        name TEXT NULL
+      );
+      CREATE INDEX idx_waypoints_route ON waypoints (routeId);
+    ''');
+    raw.execute('''
+      INSERT INTO route_plans (id, name, createdAt) VALUES (1, 'Existing route', 8000);
+    ''');
+    raw.execute('PRAGMA user_version = 3;');
+    raw.close();
+
+    final db = AppDatabase(NativeDatabase(dbFile));
+    addTearDown(db.close);
+
+    // The pre-existing route survives with the new column defaulting to false.
+    final existing = await db.getRoutePlan(1);
+    expect(existing, isNotNull);
+    expect(existing!.isClosedLoop, isFalse);
+
+    // A freshly inserted route also reads back false by default.
+    final newId = await db.insertRoutePlan(
+      const RoutePlan(name: 'New route', createdAt: 9000),
+    );
+    expect((await db.getRoutePlan(newId))!.isClosedLoop, isFalse);
+
+    // Toggling persists.
+    await db.setRoutePlanClosedLoop(1, true);
+    expect((await db.getRoutePlan(1))!.isClosedLoop, isTrue);
+  });
 }