feat: implement dashboard widgets functionality

Backend:
- Add dashboard API router with widget endpoints
- Create dashboard schemas for widget data
- Add dashboard tests

Frontend:
- Enhance Dashboard page with widget components
- Add dashboard service for API calls
- Create reusable dashboard components

OpenSpec:
- Archive add-dashboard-widgets change
- Add dashboard capability specs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

openspec/changes/archive/2026-01-07-add-dashboard-widgets/design.md

@@ -0,0 +1,101 @@
+# Design: Dashboard Widgets
+
+## Architecture Overview
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│                    Dashboard Page                            │
+├─────────────────────────────────────────────────────────────┤
+│  ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┌────────┐ │
+│  │ My Tasks    │ │ Due This    │ │ Overdue     │ │ Done % │ │
+│  │ 12          │ │ Week: 5     │ │ 2           │ │ 78%    │ │
+│  └─────────────┘ └─────────────┘ └─────────────┘ └────────┘ │
+├─────────────────────────────────────────────────────────────┤
+│  ┌──────────────────────────┐ ┌───────────────────────────┐ │
+│  │ My Workload              │ │ Project Health            │ │
+│  │ ┌────────────────────┐   │ │ ┌───────────────────────┐ │ │
+│  │ │ 32h / 40h (80%)    │   │ │ │ 8 Healthy | 2 At Risk │ │ │
+│  │ │ ████████░░         │   │ │ │ Avg Score: 76%        │ │ │
+│  │ └────────────────────┘   │ │ └───────────────────────┘ │ │
+│  └──────────────────────────┘ └───────────────────────────┘ │
+├─────────────────────────────────────────────────────────────┤
+│  Quick Actions: [Spaces] [Workload] [Health] [Audit*]       │
+└─────────────────────────────────────────────────────────────┘
+```
+
+## API Design
+
+### GET /api/dashboard
+
+Single endpoint aggregates all dashboard data to minimize frontend requests.
+
+```typescript
+interface DashboardResponse {
+  task_stats: {
+    assigned_count: number      // Total tasks assigned to user
+    due_this_week: number       // Tasks with due_date in current week
+    overdue_count: number       // Tasks past due_date, not completed
+    completion_rate: number     // Percentage (0-100)
+  }
+  workload: {
+    allocated_hours: number
+    capacity_hours: number
+    load_percentage: number
+    load_level: 'normal' | 'warning' | 'overloaded'
+  }
+  health_summary: {
+    total_projects: number
+    healthy_count: number
+    at_risk_count: number
+    critical_count: number
+    average_health_score: number
+  }
+}
+```
+
+## Data Sources
+
+| Widget | Source | Notes |
+|--------|--------|-------|
+| Task Statistics | `pjctrl_tasks` table | Filter by assignee_id = current user |
+| Workload | Existing `WorkloadService` | Reuse get_user_workload_detail() |
+| Health Summary | Existing `HealthService` | Reuse get_dashboard() summary |
+
+## Performance Considerations
+
+1. **Single API Call**: Frontend makes one request instead of three
+2. **Query Optimization**: Task stats use COUNT queries, not full rows
+3. **Caching**: Health summary already cached in Redis (5 min TTL)
+4. **No N+1**: Avoid loading related entities for counts
+
+## Component Structure
+
+```
+frontend/src/
+├── pages/
+│   └── Dashboard.tsx          # Main page (modified)
+├── components/
+│   ├── dashboard/
+│   │   ├── StatisticsCard.tsx # Single stat card
+│   │   ├── WorkloadWidget.tsx # Workload progress bar
+│   │   ├── HealthWidget.tsx   # Health summary
+│   │   └── QuickActions.tsx   # Navigation links
+└── services/
+    └── dashboard.ts           # API service (new)
+```
+
+## Trade-offs
+
+### Decision: Single vs Multiple API Endpoints
+
+**Chosen**: Single `/api/dashboard` endpoint
+
+**Rationale**:
+- Reduces network round-trips (1 vs 3)
+- Simpler frontend loading state management
+- Data is always consistent (same timestamp)
+
+**Rejected Alternative**: Use existing endpoints directly
+- Would require 3 parallel requests
+- More complex error handling
+- Harder to ensure data consistency