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/TaskDetailModal.tsx

@@ -1,11 +1,13 @@
-import { useState, useEffect } from 'react'
+import { useState, useEffect, useCallback, useRef } from 'react'
 import api from '../services/api'
 import { Comments } from './Comments'
 import { TaskAttachments } from './TaskAttachments'
+import { SubtaskList } from './SubtaskList'
 import { UserSelect } from './UserSelect'
 import { UserSearchResult } from '../services/collaboration'
 import { customFieldsApi, CustomField, CustomValueResponse } from '../services/customFields'
 import { CustomFieldInput } from './CustomFieldInput'
+import { SkeletonList } from './Skeleton'
 
 interface Task {
   id: string
@@ -37,6 +39,7 @@ interface TaskDetailModalProps {
   isOpen: boolean
   onClose: () => void
   onUpdate: () => void
+  onSubtaskClick?: (subtaskId: string) => void
 }
 
 export function TaskDetailModal({
@@ -45,6 +48,7 @@ export function TaskDetailModal({
   isOpen,
   onClose,
   onUpdate,
+  onSubtaskClick,
 }: TaskDetailModalProps) {
   const [isEditing, setIsEditing] = useState(false)
   const [saving, setSaving] = useState(false)
@@ -69,14 +73,7 @@ export function TaskDetailModal({
   const [editCustomValues, setEditCustomValues] = useState<Record<string, string | number | null>>({})
   const [loadingCustomFields, setLoadingCustomFields] = useState(false)
 
-  // Load custom fields for the project
-  useEffect(() => {
-    if (task.project_id) {
-      loadCustomFields()
-    }
-  }, [task.project_id])
-
-  const loadCustomFields = async () => {
+  const loadCustomFields = useCallback(async () => {
     setLoadingCustomFields(true)
     try {
       const response = await customFieldsApi.getCustomFields(task.project_id)
@@ -86,7 +83,14 @@ export function TaskDetailModal({
     } finally {
       setLoadingCustomFields(false)
     }
-  }
+  }, [task.project_id])
+
+  // Load custom fields for the project
+  useEffect(() => {
+    if (task.project_id) {
+      loadCustomFields()
+    }
+  }, [task.project_id, loadCustomFields])
 
   // Initialize custom values from task
   useEffect(() => {
@@ -120,6 +124,28 @@ export function TaskDetailModal({
     setIsEditing(false)
   }, [task])
 
+  // Reference to the modal overlay for focus management
+  const overlayRef = useRef<HTMLDivElement>(null)
+
+  // Handle Escape key to close modal
+  useEffect(() => {
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if (e.key === 'Escape' && isOpen) {
+        onClose()
+      }
+    }
+
+    if (isOpen) {
+      document.addEventListener('keydown', handleKeyDown)
+      // Focus the overlay for keyboard accessibility
+      overlayRef.current?.focus()
+    }
+
+    return () => {
+      document.removeEventListener('keydown', handleKeyDown)
+    }
+  }, [isOpen, onClose])
+
   if (!isOpen) return null
 
   const handleSave = async () => {
@@ -204,7 +230,15 @@ export function TaskDetailModal({
   }
 
   return (
-    <div style={styles.overlay} onClick={handleOverlayClick}>
+    <div
+      ref={overlayRef}
+      style={styles.overlay}
+      onClick={handleOverlayClick}
+      tabIndex={-1}
+      role="dialog"
+      aria-modal="true"
+      aria-labelledby="task-detail-title"
+    >
       <div style={styles.modal}>
         <div style={styles.header}>
           <div style={styles.headerLeft}>
@@ -223,7 +257,7 @@ export function TaskDetailModal({
                 autoFocus
               />
             ) : (
-              <h2 style={styles.title}>{task.title}</h2>
+              <h2 id="task-detail-title" style={styles.title}>{task.title}</h2>
             )}
           </div>
           <div style={styles.headerActions}>
@@ -285,6 +319,16 @@ export function TaskDetailModal({
             <div style={styles.section}>
               <TaskAttachments taskId={task.id} />
             </div>
+
+            {/* Subtasks Section */}
+            <div style={styles.section}>
+              <SubtaskList
+                taskId={task.id}
+                projectId={task.project_id}
+                onSubtaskClick={onSubtaskClick}
+                onSubtaskCreated={onUpdate}
+              />
+            </div>
           </div>
 
           <div style={styles.sidebar}>
@@ -420,7 +464,7 @@ export function TaskDetailModal({
                 <div style={styles.customFieldsDivider} />
                 <div style={styles.customFieldsHeader}>Custom Fields</div>
                 {loadingCustomFields ? (
-                  <div style={styles.loadingText}>Loading...</div>
+                  <SkeletonList count={3} showAvatar={false} />
                 ) : (
                   customFields.map((field) => {
                     // Get the value for this field