feat: complete LOW priority code quality improvements

Backend:
- LOW-002: Add Query validation with max page size limits (100)
- LOW-003: Replace magic strings with TaskStatus.is_done flag
- LOW-004: Add 'creation' trigger type validation
- Add action_executor.py with UpdateFieldAction and AutoAssignAction

Frontend:
- LOW-005: Replace TypeScript 'any' with 'unknown' + type guards
- LOW-006: Add ConfirmModal component with A11Y support
- LOW-007: Add ToastContext for user feedback notifications
- LOW-009: Add Skeleton components (17 loading states replaced)
- LOW-010: Setup Vitest with 21 tests for ConfirmModal and Skeleton

Components updated:
- App.tsx, ProtectedRoute.tsx, Spaces.tsx, Projects.tsx, Tasks.tsx
- ProjectSettings.tsx, AuditPage.tsx, WorkloadPage.tsx, ProjectHealthPage.tsx
- Comments.tsx, AttachmentList.tsx, TriggerList.tsx, TaskDetailModal.tsx
- NotificationBell.tsx, BlockerDialog.tsx, CalendarView.tsx, WorkloadUserDetail.tsx

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

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

logs/run-20260107-212333/run.log

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+[21:23:33] Run directory: /Users/egg/Projects/PROJECT CONTORL/logs/run-20260107-212333
+[21:23:35] WARN: Optional env key not set: ENCRYPTION_MASTER_KEY
+[21:23:35] WARN: Redis not reachable at localhost:6379
+[21:23:36] Starting backend on 127.0.0.1:8000 (python: /Users/egg/miniconda3/envs/pjctrl/bin/python)...
+[21:23:36] Starting frontend on 127.0.0.1:5173...
+[21:23:36] Running health checks...
+[21:23:37] Logs: /Users/egg/Projects/PROJECT CONTORL/logs/run-20260107-212333
+[21:23:37] Backend log: /Users/egg/Projects/PROJECT CONTORL/logs/run-20260107-212333/backend.log
+[21:23:37] Frontend log: /Users/egg/Projects/PROJECT CONTORL/logs/run-20260107-212333/frontend.log
+[21:23:37] Health log: /Users/egg/Projects/PROJECT CONTORL/logs/run-20260107-212333/health.log