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/changes/archive/2026-01-04-add-watermark-feature/proposal.md

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+# Change: Add Watermark Feature
+
+## Why
+MED-009: The `Dynamic Watermarking` requirement exists in the spec but is not implemented. Downloaded files do not contain user watermarks, making it impossible to trace document leaks.
+
+## What Changes
+- Create WatermarkService for image and PDF watermarking
+- Integrate watermark generation into download flow
+- Support configurable watermark content (name, employee ID, timestamp)
+
+## Impact
+- Affected specs: document-management
+- Affected code:
+  - `backend/app/services/watermark_service.py` (new)
+  - `backend/app/api/attachments/router.py` (modify download endpoint)
+  - `backend/requirements.txt` (add Pillow, PyMuPDF)

openspec/changes/archive/2026-01-04-add-watermark-feature/specs/document-management/spec.md

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+## MODIFIED Requirements
+
+### Requirement: Dynamic Watermarking
+系統 SHALL 在下載時自動為檔案加上使用者浮水印。
+
+#### Scenario: 圖片浮水印
+- **GIVEN** 使用者下載圖片類型附件 (PNG, JPG, JPEG)
+- **WHEN** 系統處理下載請求
+- **THEN** 自動加上包含使用者姓名、工號、下載時間的浮水印
+- **AND** 浮水印位置不影響主要內容
+
+#### Scenario: PDF 浮水印
+- **GIVEN** 使用者下載 PDF 類型附件
+- **WHEN** 系統處理下載請求
+- **THEN** 每頁加上浮水印
+- **AND** 浮水印透明度適中
+
+#### Scenario: 浮水印內容
+- **GIVEN** 需要加上浮水印
+- **WHEN** 系統生成浮水印
+- **THEN** 浮水印包含：
+  - 使用者姓名
+  - 使用者工號
+  - 下載日期時間
+  - 機密等級標示（如適用）
+
+#### Scenario: 不支援的檔案類型
+- **GIVEN** 使用者下載非圖片/PDF 類型附件
+- **WHEN** 系統處理下載請求
+- **THEN** 直接提供原始檔案下載
+- **AND** 不嘗試加上浮水印
+
+#### Scenario: 浮水印服務異常處理
+- **GIVEN** 浮水印生成過程發生錯誤
+- **WHEN** 系統無法完成浮水印處理
+- **THEN** 記錄錯誤日誌
+- **AND** 提供原始檔案下載（降級處理）

openspec/changes/archive/2026-01-04-add-watermark-feature/tasks.md

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+# Tasks: add-watermark-feature
+
+## Phase 1: Backend - Dependencies & Service
+
+- [x] 1.1 Add Pillow and PyMuPDF (fitz) to requirements.txt
+- [x] 1.2 Create WatermarkService class (`backend/app/services/watermark_service.py`)
+- [x] 1.3 Implement `add_image_watermark(image_path, user, output_path)` method
+- [x] 1.4 Implement `add_pdf_watermark(pdf_path, user, output_path)` method
+
+## Phase 2: Backend - Integration
+
+- [x] 2.1 Modify download endpoint to apply watermark
+- [x] 2.2 Add watermark configuration (enable/disable per project)
+- [x] 2.3 Handle unsupported file types gracefully (skip watermark)
+
+## Phase 3: Backend - Testing
+
+- [x] 3.1 Unit tests for image watermarking
+- [x] 3.2 Unit tests for PDF watermarking
+- [x] 3.3 Integration tests for download with watermark
+
+## Validation Criteria
+
+- Downloaded images contain visible watermark with user info
+- Downloaded PDFs have watermark on each page
+- Watermark includes: user name, employee ID, download timestamp
+- Non-image/PDF files download without modification