feat: complete issue fixes and implement remaining features

## Critical Issues (CRIT-001~003) - All Fixed
- JWT secret key validation with pydantic field_validator
- Login audit logging for success/failure attempts
- Frontend API path prefix removal

## High Priority Issues (HIGH-001~008) - All Fixed
- Project soft delete using is_active flag
- Redis session token bytes handling
- Rate limiting with slowapi (5 req/min for login)
- Attachment API permission checks
- Kanban view with drag-and-drop
- Workload heatmap UI (WorkloadPage, WorkloadHeatmap)
- TaskDetailModal integrating Comments/Attachments
- UserSelect component for task assignment

## Medium Priority Issues (MED-001~012) - All Fixed
- MED-001~005: DB commits, N+1 queries, datetime, error format, blocker flag
- MED-006: Project health dashboard (HealthService, ProjectHealthPage)
- MED-007: Capacity update API (PUT /api/users/{id}/capacity)
- MED-008: Schedule triggers (cron parsing, deadline reminders)
- MED-009: Watermark feature (image/PDF watermarking)
- MED-010~012: useEffect deps, DOM operations, PDF export

## New Files
- backend/app/api/health/ - Project health API
- backend/app/services/health_service.py
- backend/app/services/trigger_scheduler.py
- backend/app/services/watermark_service.py
- backend/app/core/rate_limiter.py
- frontend/src/pages/ProjectHealthPage.tsx
- frontend/src/components/ProjectHealthCard.tsx
- frontend/src/components/KanbanBoard.tsx
- frontend/src/components/WorkloadHeatmap.tsx

## Tests
- 113 new tests passing (health: 32, users: 14, triggers: 35, watermark: 32)

## OpenSpec Archives
- add-project-health-dashboard
- add-capacity-update-api
- add-schedule-triggers
- add-watermark-feature
- add-rate-limiting
- enhance-frontend-ux
- add-resource-management-ui

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

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

openspec/specs/resource-management/spec.md

@@ -50,6 +50,18 @@
 - **THEN** `load_percentage` 顯示為 `null`
 - **AND** `load_level` 顯示為 `unavailable`
 
+#### Scenario: 容量更新 API
+- **GIVEN** 管理者需要更新團隊成員的容量
+- **WHEN** 管理者呼叫 `PUT /api/users/{user_id}/capacity` 並提供新容量值
+- **THEN** 系統驗證容量值在有效範圍內 (0-168 小時)
+- **AND** 更新使用者的 capacity 欄位
+- **AND** 記錄變更至稽核日誌
+
+#### Scenario: 容量更新權限控制
+- **GIVEN** 一般使用者嘗試更新他人容量
+- **WHEN** 使用者呼叫 `PUT /api/users/{other_id}/capacity`
+- **THEN** 系統拒絕請求並回傳 403 Forbidden
+
 ### Requirement: Multi-Project Health Dashboard
 系統 SHALL 提供多專案健康看板，讓主管一覽所有專案狀態。
 
@@ -65,6 +77,18 @@
 - **THEN** 該專案標示為延遲狀態
 - **AND** 顯示延遲任務數量與影響
 
+#### Scenario: 專案健康 API
+- **GIVEN** 後端系統運行中
+- **WHEN** 客戶端請求 `GET /api/projects/health`
+- **THEN** 系統回傳所有可存取專案的健康數據
+- **AND** 包含 `total_tasks`, `completed_tasks`, `overdue_tasks`, `blocked_tasks`, `risk_score`
+
+#### Scenario: 單一專案健康詳情
+- **GIVEN** 主管需要查看特定專案詳情
+- **WHEN** 客戶端請求 `GET /api/projects/{id}/health`
+- **THEN** 系統回傳該專案的詳細健康數據
+- **AND** 包含任務分類統計與風險評估
+
 ### Requirement: Team Workload Distribution
 
 系統 SHALL 提供團隊工作分配查詢功能。
@@ -99,6 +123,31 @@
 - **WHEN** 查詢其他部門使用者的負載
 - **THEN** 系統拒絕存取並回傳 403 Forbidden
 
+### Requirement: Workload Heatmap UI
+The system SHALL provide a visual workload heatmap interface for managers.
+
+#### Scenario: View workload heatmap
+- **GIVEN** user is logged in as manager or admin
+- **WHEN** user navigates to /workload page
+- **THEN** system displays a heatmap showing all accessible users' workload
+- **AND** each user cell is color-coded by load level (green/yellow/red)
+
+#### Scenario: Navigate between weeks
+- **GIVEN** user is viewing the workload page
+- **WHEN** user clicks previous/next week buttons
+- **THEN** the heatmap updates to show that week's workload data
+
+#### Scenario: View user workload details
+- **GIVEN** user is viewing the workload heatmap
+- **WHEN** user clicks on a specific user's cell
+- **THEN** a modal/drawer opens showing that user's task breakdown
+- **AND** tasks show title, project, time estimate, and due date
+
+#### Scenario: Filter by department
+- **GIVEN** user is a system admin
+- **WHEN** user selects a department from the filter
+- **THEN** the heatmap shows only users from that department
+
 ## Data Model
 
 ```