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-enhance-frontend-ux/specs/task-management/spec.md

@@ -0,0 +1,58 @@
+## ADDED Requirements
+
+### Requirement: Kanban View
+The system SHALL provide a Kanban board view for tasks with drag-and-drop status management.
+
+#### Scenario: View Kanban board
+- **GIVEN** user is on the Tasks page
+- **WHEN** user selects Kanban view
+- **THEN** tasks are displayed in columns grouped by status
+- **AND** each column header shows the status name and task count
+
+#### Scenario: Drag task to change status
+- **GIVEN** user is viewing the Kanban board
+- **WHEN** user drags a task card to a different status column
+- **THEN** the task status is updated via API
+- **AND** the card moves to the new column
+- **AND** other users viewing the board see the update
+
+#### Scenario: View toggle persistence
+- **GIVEN** user switches to Kanban view
+- **WHEN** user navigates away and returns
+- **THEN** the Kanban view is still selected
+
+### Requirement: Task Detail Modal
+The system SHALL provide a task detail modal with comments and attachments.
+
+#### Scenario: Open task detail
+- **GIVEN** user is viewing tasks in any view
+- **WHEN** user clicks on a task
+- **THEN** a modal opens showing task details
+- **AND** the modal includes comments section
+- **AND** the modal includes attachments section
+
+#### Scenario: Edit task in modal
+- **GIVEN** user has task detail modal open
+- **WHEN** user modifies task fields and saves
+- **THEN** the task is updated via API
+- **AND** the task list/board reflects the changes
+
+### Requirement: Task Assignment UI
+The system SHALL allow assigning tasks to users during creation and editing.
+
+#### Scenario: Assign task during creation
+- **GIVEN** user is creating a new task
+- **WHEN** user selects an assignee from the dropdown
+- **THEN** the task is created with the selected assignee
+
+#### Scenario: Change task assignee
+- **GIVEN** user has task detail modal open
+- **WHEN** user changes the assignee
+- **THEN** the task assignee is updated
+- **AND** the new assignee receives a notification
+
+#### Scenario: Set due date and time estimate
+- **GIVEN** user is creating or editing a task
+- **WHEN** user sets due date and time estimate
+- **THEN** the values are saved with the task
+- **AND** the task appears on the appropriate date in calendar view