feat(platform-service): add GET /settings/kill-switch public endpoint

- No auth required — mobile apps call this at launch before login
- Reads kill_switch feature flag from Cosmos DB
- If flag enabled=true → returns disabled:true with maintenance message
- Fail-open: DB errors allow app to run normally
- Response: { enabled: bool, disabled: bool, message: string }

Used by iOS KillSwitchService.swift and Android KillSwitchService.kt

services/platform-service/src/modules/settings/routes.ts

@@ -1,6 +1,7 @@
 /**
  * User settings REST endpoints.
  *
+ * GET    /settings/kill-switch       — public kill switch check (no auth)
  * GET    /settings                   — get user settings
  * PUT    /settings                   — merge global settings
  * GET    /settings/device/:deviceId  — get resolved settings for a device
@@ -13,6 +14,7 @@ import { getRequestProductId } from '../../lib/request-context.js';
 import { BadRequestError, UnauthorizedError } from '../../lib/errors.js';
 import * as repo from './repository.js';
 import { UpdateSettingsSchema, SetDeviceOverridesSchema, type UserSettingsDoc } from './types.js';
+import * as flagRepo from '../flags/repository.js';
 
 function getRequestUserId(req: FastifyRequest): string {
   const userId = req.jwtPayload?.sub;
@@ -34,6 +36,32 @@ function buildDefaultDoc(productId: string, userId: string): UserSettingsDoc {
 }
 
 export async function settingsRoutes(app: FastifyInstance) {
+  // Public kill switch endpoint — no auth required.
+  // Mobile apps call this at launch to check if the app is disabled.
+  // Reads the `kill_switch` feature flag: if enabled=true → app is disabled.
+  app.get('/settings/kill-switch', async req => {
+    const productId =
+      (req.query as { productId?: string }).productId ||
+      (req.headers['x-product-id'] as string) ||
+      process.env.PRODUCT_ID ||
+      '';
+    if (!productId) return { enabled: true, disabled: false, message: '' };
+
+    try {
+      const flag = await flagRepo.getByKey('kill_switch', productId);
+      if (flag && flag.enabled) {
+        return {
+          enabled: false,
+          disabled: true,
+          message: flag.description || 'LysnrAI is temporarily unavailable for maintenance.',
+        };
+      }
+    } catch {
+      // DB error — fail open (allow app to run)
+    }
+    return { enabled: true, disabled: false, message: '' };
+  });
+
   app.get('/settings', async req => {
     const productId = getRequestProductId(req);
     const userId = getRequestUserId(req);