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>

backend/app/schemas/dashboard.py

@@ -0,0 +1,72 @@
+"""Dashboard API schemas.
+
+Defines response models for the dashboard endpoint that aggregates
+task statistics, workload, and project health summaries.
+"""
+from pydantic import BaseModel
+from decimal import Decimal
+from typing import Optional
+
+from app.schemas.workload import LoadLevel
+
+
+class TaskStatistics(BaseModel):
+    """User's task statistics for dashboard display.
+
+    Attributes:
+        assigned_count: Total tasks assigned to user (not completed)
+        due_this_week: Tasks with due_date in current week
+        overdue_count: Tasks past due_date, not completed
+        completion_rate: Percentage of completed tasks (0-100)
+    """
+    assigned_count: int
+    due_this_week: int
+    overdue_count: int
+    completion_rate: float
+
+
+class WorkloadSummary(BaseModel):
+    """User's workload summary for dashboard display.
+
+    Attributes:
+        allocated_hours: Total estimated hours from tasks due this week
+        capacity_hours: User's weekly capacity
+        load_percentage: Percentage of capacity used
+        load_level: normal (<80%), warning (80-99%), overloaded (>=100%)
+    """
+    allocated_hours: Decimal
+    capacity_hours: Decimal
+    load_percentage: Optional[Decimal] = None
+    load_level: LoadLevel
+
+
+class HealthSummary(BaseModel):
+    """Aggregated project health summary for dashboard display.
+
+    Attributes:
+        total_projects: Total number of active projects
+        healthy_count: Projects with health_score >= 80
+        at_risk_count: Projects with health_score 50-79
+        critical_count: Projects with health_score < 50
+        average_health_score: Average health score across all projects
+    """
+    total_projects: int
+    healthy_count: int
+    at_risk_count: int
+    critical_count: int
+    average_health_score: float
+
+
+class DashboardResponse(BaseModel):
+    """Complete dashboard response aggregating all widgets.
+
+    Single endpoint response that combines:
+    - Task statistics for the current user
+    - Current week workload summary
+    - Project health summary
+
+    This minimizes frontend API calls and ensures data consistency.
+    """
+    task_stats: TaskStatistics
+    workload: WorkloadSummary
+    health_summary: HealthSummary