feat: Add time block approval workflow and staff permission system

- Add TimeBlock approval status with manager approval workflow
- Create core mixins for staff permission restrictions (DenyStaffWritePermission, etc.)
- Add StaffDashboard page for staff-specific views
- Refactor MyAvailability page for time block management
- Update field mobile status machine and views
- Add per-user permission overrides via JSONField
- Document core mixins and permission system in CLAUDE.md

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

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

frontend/src/components/StaffPermissions.tsx

@@ -87,6 +87,15 @@ export const PERMISSION_CONFIGS: PermissionConfig[] = [
     defaultValue: true,
     roles: ['staff'],
   },
+  {
+    key: 'can_self_approve_time_off',
+    labelKey: 'staff.canSelfApproveTimeOff',
+    labelDefault: 'Can self-approve time off',
+    hintKey: 'staff.canSelfApproveTimeOffHint',
+    hintDefault: 'Add time off without requiring manager/owner approval',
+    defaultValue: false,
+    roles: ['staff'],
+  },
   // Shared permissions (both manager and staff)
   {
     key: 'can_access_tickets',