feat: implement workload heatmap module

- Backend (FastAPI):
  - Workload heatmap API with load level calculation
  - User workload detail endpoint with task breakdown
  - Redis caching for workload calculations (1hr TTL)
  - Department isolation and access control
  - WorkloadSnapshot model for historical data
  - Alembic migration for workload_snapshots table

- API Endpoints:
  - GET /api/workload/heatmap - Team workload overview
  - GET /api/workload/user/{id} - User workload detail
  - GET /api/workload/me - Current user workload

- Load Levels:
  - normal: <80%, warning: 80-99%, overloaded: >=100%

- Tests:
  - 26 unit/API tests
  - 15 E2E automated tests
  - 77 total tests passing

- OpenSpec:
  - add-resource-workload change archived
  - resource-management spec updated

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

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

backend/app/schemas/workload.py

@@ -0,0 +1,78 @@
+from pydantic import BaseModel
+from typing import Optional, List
+from datetime import date, datetime
+from decimal import Decimal
+from enum import Enum
+
+
+class LoadLevel(str, Enum):
+    """Workload level classification."""
+    NORMAL = "normal"
+    WARNING = "warning"
+    OVERLOADED = "overloaded"
+    UNAVAILABLE = "unavailable"
+
+
+class TaskWorkloadInfo(BaseModel):
+    """Task information for workload detail view."""
+    task_id: str
+    title: str
+    project_id: str
+    project_name: str
+    due_date: Optional[datetime] = None
+    original_estimate: Optional[Decimal] = None
+    status: Optional[str] = None
+
+
+class UserWorkloadSummary(BaseModel):
+    """Summary of a user's workload for heatmap display."""
+    user_id: str
+    user_name: str
+    department_id: Optional[str] = None
+    department_name: Optional[str] = None
+    capacity_hours: Decimal
+    allocated_hours: Decimal
+    load_percentage: Optional[Decimal] = None
+    load_level: LoadLevel
+    task_count: int
+
+
+class WorkloadHeatmapResponse(BaseModel):
+    """Response for workload heatmap API."""
+    week_start: date
+    week_end: date
+    users: List[UserWorkloadSummary]
+
+
+class UserWorkloadDetail(BaseModel):
+    """Detailed workload for a specific user."""
+    user_id: str
+    user_name: str
+    week_start: date
+    week_end: date
+    capacity_hours: Decimal
+    allocated_hours: Decimal
+    load_percentage: Optional[Decimal] = None
+    load_level: LoadLevel
+    tasks: List[TaskWorkloadInfo]
+
+
+class WorkloadSnapshotResponse(BaseModel):
+    """Response for workload snapshot."""
+    id: str
+    user_id: str
+    week_start: date
+    allocated_hours: Decimal
+    capacity_hours: Decimal
+    load_percentage: Decimal
+    task_count: int
+    created_at: datetime
+    updated_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class CapacityUpdate(BaseModel):
+    """Request to update user capacity."""
+    capacity: Decimal