feat(mobile): bootstrap mobile app (PWA + Capacitor + backend auth/CORS)

Implements the §12 bootstrap from docs/mobile-app-plan.md.

Backend (§6):
- auth: optional returnToken flag on login returns the JWT in the body
  (data.authToken) for native Keychain/Keystore + Bearer; web cookie flow
  unchanged.
- main.ts: explicit CORS allowlist (APP_URL + CORS_ALLOWED_ORIGINS env +
  Capacitor WebView origins), credentials enabled, replaces open enableCors().
- optional OpenAPI/Swagger at /api/docs behind SWAGGER_ENABLED.
- env: CORS_ALLOWED_ORIGINS, SWAGGER_ENABLED, CAP_SERVER_URL.

PWA:
- manifest metadata, hand-rolled service worker (network-first nav, SWR
  assets, never intercepts /api,/socket.io,/collab), prod-only registration,
  apple-touch-icon.

Capacitor:
- capacitor.config.ts (webDir apps/client/dist; iOS via CAP_SERVER_URL to
  avoid bundling the AGPL client in the .ipa, see plan §9), cap:* scripts,
  deps, .gitignore for native dirs.
- docs/mobile-bootstrap.md documenting what is done and the remaining manual
  steps (cap add ios/android, APNs/FCM, stores).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/core/auth/auth.controller.ts

@@ -97,6 +97,12 @@ export class AuthController {
         } else if (mfaResult.authToken) {
           // User doesn't have MFA and workspace doesn't require it
           this.setAuthCookie(res, mfaResult.authToken);
+          // Opt-in body token for native clients (Bearer auth). The response is
+          // wrapped by TransformHttpResponseInterceptor, so clients read it at
+          // `data.authToken`. Web clients omit returnToken and keep the cookie.
+          if (loginInput.returnToken) {
+            return { authToken: mfaResult.authToken };
+          }
           return;
         }
       }
@@ -104,6 +110,12 @@ export class AuthController {
 
     const authToken = await this.authService.login(loginInput, workspace.id);
     this.setAuthCookie(res, authToken);
+    // Opt-in body token for native clients (Bearer auth). The response is wrapped
+    // by TransformHttpResponseInterceptor, so clients read it at `data.authToken`.
+    // Web clients omit returnToken and keep using the httpOnly cookie only.
+    if (loginInput.returnToken) {
+      return { authToken };
+    }
   }
 
   @UseGuards(SetupGuard)