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-schedule-triggers/proposal.md

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+# Change: Add Schedule Triggers
+
+## Why
+MED-008: The `Trigger Conditions` requirement includes time-based triggers (cron expressions), but the execution logic is not implemented. The scheduler setup exists for weekly reports but schedule-type triggers cannot be executed.
+
+## What Changes
+- Implement cron expression parsing for schedule triggers
+- Add scheduler job for evaluating schedule triggers
+- Support deadline reminder triggers
+
+## Impact
+- Affected specs: automation
+- Affected code:
+  - `backend/app/services/trigger_service.py` (modify)
+  - `backend/app/services/trigger_scheduler.py` (new)
+  - `backend/app/scheduler.py` (modify)

openspec/changes/archive/2026-01-04-add-schedule-triggers/specs/automation/spec.md

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+## MODIFIED Requirements
+
+### Requirement: Trigger Conditions
+系統 SHALL 支援多種觸發條件類型。
+
+#### Scenario: 欄位變更條件
+- **GIVEN** 觸發器設定為「當 Status 欄位變更為特定值」
+- **WHEN** 任務的 Status 欄位變更為該值
+- **THEN** 觸發器被觸發
+
+#### Scenario: 時間條件
+- **GIVEN** 觸發器設定為「每週五下午 4:00」
+- **WHEN** 系統時間達到設定時間
+- **THEN** 觸發器被觸發
+
+#### Scenario: 複合條件
+- **GIVEN** 觸發器設定為「當 Status = 完成 且 Priority = 高」
+- **WHEN** 任務同時滿足兩個條件
+- **THEN** 觸發器被觸發
+
+#### Scenario: Cron 表達式觸發
+- **GIVEN** 觸發器設定為 cron 表達式 (如 `0 9 * * 1` 每週一早上 9 點)
+- **WHEN** 系統時間匹配 cron 表達式
+- **THEN** 系統評估並執行該觸發器
+- **AND** 記錄執行結果至 trigger_logs
+
+#### Scenario: 截止日期提醒
+- **GIVEN** 觸發器設定為「截止日前 N 天提醒」
+- **WHEN** 任務距離截止日剩餘 N 天
+- **THEN** 系統發送提醒通知給任務指派者
+- **AND** 每個任務每個提醒設定只觸發一次

openspec/changes/archive/2026-01-04-add-schedule-triggers/tasks.md

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+# Tasks: add-schedule-triggers
+
+## Phase 1: Backend - Cron Support
+
+- [x] 1.1 Add croniter dependency to requirements.txt
+- [x] 1.2 Create TriggerSchedulerService (`backend/app/services/trigger_scheduler.py`)
+- [x] 1.3 Implement cron expression validation in trigger creation
+- [x] 1.4 Implement `evaluate_schedule_triggers()` method
+
+## Phase 2: Backend - Scheduler Integration
+
+- [x] 2.1 Add scheduled job to evaluate schedule triggers (every minute)
+- [x] 2.2 Implement deadline reminder logic (check tasks N days before due)
+- [x] 2.3 Update trigger logs for schedule trigger executions
+
+## Phase 3: Backend - Testing
+
+- [x] 3.1 Unit tests for cron expression parsing
+- [x] 3.2 Unit tests for deadline reminder logic
+- [x] 3.3 Integration tests for schedule trigger execution
+
+## Validation Criteria
+
+- [x] Cron expressions are validated on trigger creation
+- [x] Schedule triggers execute at specified times
+- [x] Deadline reminders sent N days before task due date