feat(messaging): Add broadcast messaging system for owners and managers

- Add BroadcastMessage and MessageRecipient models for sending messages to groups or individuals
- Add Messages page with compose form and sent messages list
- Support targeting by role (owners, managers, staff, customers) or individual users
- Add can_send_messages permission (owners always, managers by default with revocable permission)
- Add autofill search dropdown with infinite scroll for selecting individual recipients
- Add staff permission toggle for managers' messaging access
- Integrate Messages link in sidebar for users with permission

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

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

frontend/src/i18n/locales/en.json

@@ -491,9 +491,31 @@
     "reactivateAccount": "Reactivate Account",
     "deactivateHint": "Prevent this user from logging in while keeping their data",
     "reactivateHint": "Allow this user to log in again",
+    "canSendMessages": "Can send broadcast messages",
+    "canSendMessagesHint": "Send messages to groups of staff and customers",
     "deactivate": "Deactivate",
+    "canInviteStaff": "Can invite new staff members",
+    "canInviteStaffHint": "Allow this manager to send invitations to new staff members",
+    "canManageResources": "Can manage resources",
+    "canManageResourcesHint": "Create, edit, and delete bookable resources",
+    "canManageServices": "Can manage services",
+    "canManageServicesHint": "Create, edit, and delete service offerings",
+    "canViewReports": "Can view reports",
+    "canViewReportsHint": "Access business analytics and financial reports",
+    "canAccessSettings": "Can access business settings",
+    "canAccessSettingsHint": "Modify business profile, branding, and configuration",
+    "canRefundPayments": "Can refund payments",
+    "canRefundPaymentsHint": "Process refunds for customer payments",
+    "canViewAllSchedules": "Can view all schedules",
+    "canViewAllSchedulesHint": "View schedules of other staff members (otherwise only their own)",
+    "canManageOwnAppointments": "Can manage own appointments",
+    "canManageOwnAppointmentsHint": "Create, reschedule, and cancel their own appointments",
     "canSelfApproveTimeOff": "Can self-approve time off",
-    "canSelfApproveTimeOffHint": "Add time off without requiring manager/owner approval"
+    "canSelfApproveTimeOffHint": "Add time off without requiring manager/owner approval",
+    "canAccessTickets": "Can access support tickets",
+    "canAccessTicketsHint": "View and manage customer support tickets",
+    "managerPermissions": "Manager Permissions",
+    "staffPermissions": "Staff Permissions"
   },
   "staffDashboard": {
     "welcomeTitle": "Welcome, {{name}}!",