Add milestone data layer and redesign Projects tab

Milestone data layer:
- lib/data/models/milestone.dart: Milestone model with progress fields
  (total, completed, pct) from backend progress endpoint
- lib/data/api/milestones_api.dart: CRUD client for
  /api/projects/:id/milestones
- lib/data/repositories/milestones_repository.dart: thin repository wrapper
- lib/providers/milestones_provider.dart: FutureProvider.family keyed by
  project ID — lazily fetched per project when expanded
- api_client_provider.dart: registers milestonesApiProvider and
  milestonesRepositoryProvider

Projects tab redesign (project_list_screen.dart):
- Each project is now an ExpansionTile showing open task count in subtitle
- Expanding a project fetches its milestones and groups tasks under milestone
  headers with inline progress bar (completed/total count)
- Tasks show status icon, due date with overdue highlighting, priority dot
- 'No milestone' section at bottom for unassigned tasks
- Tapping a task navigates to the task editor
- Long-press on project title opens archive/complete/delete bottom sheet
- 'New task' button at bottom of each expanded project section

Bump version to 26.03.02+1

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

lib/data/api/milestones_api.dart

@@ -0,0 +1,71 @@
+import 'package:dio/dio.dart';
+
+import '../models/milestone.dart';
+import 'api_client.dart';
+
+class MilestonesApi {
+  final Dio _dio;
+  const MilestonesApi(this._dio);
+
+  Future<List<Milestone>> getAll(int projectId, {String? status}) async {
+    try {
+      final response = await _dio.get(
+        '/api/projects/$projectId/milestones',
+        queryParameters: status != null ? {'status': status} : null,
+      );
+      final data = response.data as Map<String, dynamic>;
+      final list = data['milestones'] as List<dynamic>;
+      return list
+          .map((e) => Milestone.fromJson(e as Map<String, dynamic>))
+          .toList();
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+
+  Future<Milestone> create(
+    int projectId, {
+    required String title,
+    String? description,
+    int orderIndex = 0,
+  }) async {
+    try {
+      final response = await _dio.post(
+        '/api/projects/$projectId/milestones',
+        data: {
+          'title': title,
+          if (description != null && description.isNotEmpty)
+            'description': description,
+          'order_index': orderIndex,
+        },
+      );
+      return Milestone.fromJson(response.data as Map<String, dynamic>);
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+
+  Future<Milestone> update(
+    int projectId,
+    int milestoneId,
+    Map<String, dynamic> fields,
+  ) async {
+    try {
+      final response = await _dio.patch(
+        '/api/projects/$projectId/milestones/$milestoneId',
+        data: fields,
+      );
+      return Milestone.fromJson(response.data as Map<String, dynamic>);
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+
+  Future<void> delete(int projectId, int milestoneId) async {
+    try {
+      await _dio.delete('/api/projects/$projectId/milestones/$milestoneId');
+    } on DioException catch (e) {
+      throw dioToApp(e);
+    }
+  }
+}