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>

pubspec.yaml

@@ -2,7 +2,7 @@ name: fabled_app
 description: "FabledAssistant mobile client for Android."
 publish_to: 'none'
 
-version: 26.03.01+1
+version: 26.03.02+1
 
 environment:
   sdk: ^3.11.0