feat(web): TODO-001 kill switch maintenance banner + disable timer creation

web/src/app/providers.tsx

@@ -1,34 +1,32 @@
 'use client';
 
-import { useEffect } from 'react';
+import { createContext, useContext, useEffect, useState } from 'react';
 import { usePathname } from 'next/navigation';
 import { AuthProvider } from '@/lib/auth-context';
 import { initTelemetry, trackPageView } from '@/lib/telemetry';
 import { initFeatureFlags } from '@/lib/feature-flags';
 import { initDiagnostics } from '@/lib/diagnostics';
 import { checkKillSwitch } from '@/lib/kill-switch';
+import { MaintenanceBanner } from '@/components/MaintenanceBanner';
 import { ToastProvider } from '@bytelyst/ui';
 import type { ReactNode } from 'react';
 
+const MaintenanceContext = createContext(false);
+
+export function useMaintenanceMode(): boolean {
+  return useContext(MaintenanceContext);
+}
+
 export function Providers({ children }: { children: ReactNode }) {
   const pathname = usePathname();
+  const [isMaintenanceMode, setIsMaintenanceMode] = useState(false);
 
   useEffect(() => {
     initTelemetry();
     initFeatureFlags();
     initDiagnostics();
-    // TODO-001: Kill switch maintenance banner
-    // Priority: medium | Phase: 0
-    // When checkKillSwitch() returns disabled=true:
-    //   1. Set a React state flag (e.g. `isMaintenanceMode`)
-    //   2. Render a <MaintenanceBanner /> component at the top of the app
-    //   3. Disable timer creation buttons (pass flag via context or prop)
-    //   4. Use --cm-warning-* design tokens for the banner styling
-    // File to create: web/src/components/MaintenanceBanner.tsx
     checkKillSwitch().then((disabled) => {
-      if (disabled) {
-        // TODO-001: Surface this in the UI (see instructions above)
-      }
+      setIsMaintenanceMode(disabled);
     });
   }, []);
 
@@ -40,7 +38,12 @@ export function Providers({ children }: { children: ReactNode }) {
 
   return (
     <AuthProvider>
-      <ToastProvider>{children}</ToastProvider>
+      <MaintenanceContext.Provider value={isMaintenanceMode}>
+        <ToastProvider>
+          {isMaintenanceMode && <MaintenanceBanner />}
+          {children}
+        </ToastProvider>
+      </MaintenanceContext.Provider>
     </AuthProvider>
   );
 }

web/src/components/CreateTimerModal.tsx

@@ -7,6 +7,7 @@ import type { UrgencyLevel } from '@/lib/urgency';
 import { CASCADE_PRESET_LABELS } from '@/lib/cascade';
 import type { CascadePreset } from '@/lib/cascade';
 import { X, AlarmClock, Timer, Coffee, Sparkles, CalendarDays } from 'lucide-react';
+import { useMaintenanceMode } from '@/app/providers';
 import { BUILT_IN_CATEGORIES, getCategoryById } from '@/lib/categories';
 import { parseNaturalLanguage } from '@/lib/nl-parser';
 import type { ParseResult } from '@/lib/nl-parser';
@@ -21,6 +22,7 @@ interface CreateTimerModalProps {
 
 export function CreateTimerModal({ isOpen, onClose }: CreateTimerModalProps) {
   const { addAlarm, addCountdown, addPomodoro, addEvent } = useTimerStore();
+  const maintenanceMode = useMaintenanceMode();
 
   const [tab, setTab] = useState<TabType>('countdown');
   const [nlInput, setNlInput] = useState('');
@@ -570,13 +572,14 @@ export function CreateTimerModal({ isOpen, onClose }: CreateTimerModalProps) {
           {/* Create button */}
           <button
             onClick={handleCreate}
-            className="w-full py-3 rounded-xl text-sm font-semibold transition-colors cursor-pointer"
+            disabled={maintenanceMode}
+            className="w-full py-3 rounded-xl text-sm font-semibold transition-colors cursor-pointer disabled:opacity-40 disabled:cursor-not-allowed"
             style={{
               backgroundColor: 'var(--cm-accent)',
               color: 'var(--cm-white)',
             }}
           >
-            Create {tab === 'pomodoro' ? 'Pomodoro' : tab === 'alarm' ? 'Alarm' : 'Countdown'}
+            {maintenanceMode ? 'Timer creation disabled (maintenance)' : `Create ${tab === 'pomodoro' ? 'Pomodoro' : tab === 'alarm' ? 'Alarm' : 'Countdown'}`}
           </button>
         </div>
       </div>

web/src/components/MaintenanceBanner.tsx

@@ -0,0 +1,25 @@
+'use client';
+
+import { AlertTriangle } from 'lucide-react';
+
+interface MaintenanceBannerProps {
+  message?: string;
+}
+
+export function MaintenanceBanner({ message }: MaintenanceBannerProps) {
+  return (
+    <div
+      role="alert"
+      aria-label="Maintenance mode active"
+      className="w-full px-4 py-3 flex items-center justify-center gap-2 text-sm font-medium"
+      style={{
+        backgroundColor: 'var(--cm-important-15)',
+        color: 'var(--cm-important)',
+        borderBottom: '1px solid var(--cm-important)',
+      }}
+    >
+      <AlertTriangle size={16} aria-hidden="true" />
+      <span>{message || 'ChronoMind is currently in maintenance mode. Timer creation is temporarily disabled.'}</span>
+    </div>
+  );
+}