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>

frontend/src/components/ConfirmModal.tsx

@@ -0,0 +1,155 @@
+import { useEffect, useRef } from 'react'
+
+interface ConfirmModalProps {
+  isOpen: boolean
+  title: string
+  message: string
+  confirmText?: string
+  cancelText?: string
+  confirmStyle?: 'danger' | 'primary'
+  onConfirm: () => void
+  onCancel: () => void
+}
+
+export function ConfirmModal({
+  isOpen,
+  title,
+  message,
+  confirmText = 'Confirm',
+  cancelText = 'Cancel',
+  confirmStyle = 'danger',
+  onConfirm,
+  onCancel,
+}: ConfirmModalProps) {
+  const modalOverlayRef = useRef<HTMLDivElement>(null)
+  const confirmButtonRef = useRef<HTMLButtonElement>(null)
+
+  // A11Y: Handle Escape key to close modal
+  useEffect(() => {
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if (e.key === 'Escape' && isOpen) {
+        onCancel()
+      }
+    }
+
+    if (isOpen) {
+      document.addEventListener('keydown', handleKeyDown)
+      // Focus confirm button when modal opens
+      confirmButtonRef.current?.focus()
+    }
+
+    return () => {
+      document.removeEventListener('keydown', handleKeyDown)
+    }
+  }, [isOpen, onCancel])
+
+  if (!isOpen) return null
+
+  const handleOverlayClick = (e: React.MouseEvent) => {
+    if (e.target === e.currentTarget) {
+      onCancel()
+    }
+  }
+
+  return (
+    <div
+      ref={modalOverlayRef}
+      style={styles.overlay}
+      onClick={handleOverlayClick}
+      role="dialog"
+      aria-modal="true"
+      aria-labelledby="confirm-modal-title"
+      aria-describedby="confirm-modal-message"
+    >
+      <div style={styles.modal}>
+        <h2 id="confirm-modal-title" style={styles.title}>
+          {title}
+        </h2>
+        <p id="confirm-modal-message" style={styles.message}>
+          {message}
+        </p>
+        <div style={styles.actions}>
+          <button onClick={onCancel} style={styles.cancelButton}>
+            {cancelText}
+          </button>
+          <button
+            ref={confirmButtonRef}
+            onClick={onConfirm}
+            style={{
+              ...styles.confirmButton,
+              ...(confirmStyle === 'danger' ? styles.dangerButton : styles.primaryButton),
+            }}
+          >
+            {confirmText}
+          </button>
+        </div>
+      </div>
+    </div>
+  )
+}
+
+const styles: Record<string, React.CSSProperties> = {
+  overlay: {
+    position: 'fixed',
+    top: 0,
+    left: 0,
+    right: 0,
+    bottom: 0,
+    backgroundColor: 'rgba(0, 0, 0, 0.5)',
+    display: 'flex',
+    justifyContent: 'center',
+    alignItems: 'center',
+    zIndex: 1200,
+  },
+  modal: {
+    backgroundColor: 'white',
+    borderRadius: '8px',
+    padding: '24px',
+    width: '400px',
+    maxWidth: '90%',
+    boxShadow: '0 8px 32px rgba(0, 0, 0, 0.2)',
+  },
+  title: {
+    margin: '0 0 12px 0',
+    fontSize: '18px',
+    fontWeight: 600,
+    color: '#212529',
+  },
+  message: {
+    margin: '0 0 24px 0',
+    fontSize: '14px',
+    color: '#495057',
+    lineHeight: 1.5,
+  },
+  actions: {
+    display: 'flex',
+    justifyContent: 'flex-end',
+    gap: '12px',
+  },
+  cancelButton: {
+    padding: '10px 20px',
+    backgroundColor: '#f8f9fa',
+    color: '#495057',
+    border: '1px solid #dee2e6',
+    borderRadius: '6px',
+    fontSize: '14px',
+    cursor: 'pointer',
+  },
+  confirmButton: {
+    padding: '10px 20px',
+    color: 'white',
+    border: 'none',
+    borderRadius: '6px',
+    fontSize: '14px',
+    fontWeight: 500,
+    cursor: 'pointer',
+  },
+  dangerButton: {
+    backgroundColor: '#dc3545',
+  },
+  primaryButton: {
+    backgroundColor: '#0066cc',
+  },
+}
+
+export default ConfirmModal