Serve the app on app.qrmaster.net, marketing on www

Splits the two hostnames across one deployment. No files move: the Next app still
serves every route on both hosts, and the middleware decides per host which paths it
owns and 301s the rest. /login and /signup stay on www - all 82 marketing CTAs point
at /signup, which carries a hard canonical to www plus ad traffic.

src/lib/hosts.ts is the single source of truth for the boundary (APP_PATH_PREFIXES,
isAppPath, wwwUrl, appUrl, urlForPath). The middleware and every absolute-URL builder
read from it so they cannot drift apart.

- Split the overloaded NEXT_PUBLIC_APP_URL into a www and an app origin. It previously
  fed both public URLs and in-app URLs, so any single value was wrong somewhere. Most
  important: QRCodeCard encodes this origin into the QR code the user downloads and
  prints, so it must stay on www.
- Route Stripe return URLs, email links and OAuth redirects per path rather than
  against one origin, so /dashboard lands on app and /pricing on www.
- Cross the host boundary once, after a successful login: the router cannot push across
  origins, so that jump needs a full load. The user arrives signed in because the
  session cookie is scoped to COOKIE_DOMAIN.
- Keep the app host out of search indexes: X-Robots-Tag on every response plus a
  Disallow-all robots.txt via rewrite, and /sitemap.xml redirects to www.
- Point the TikTok callback fallback at www explicitly. It used to read
  NEXT_PUBLIC_APP_URL, whose meaning changed here, and only the apex domain is
  verified with TikTok.

Host splitting is inert while both origins are equal, so development is unaffected.

Verified: tsc clean, production build succeeds including the Edge middleware bundle,
and the path-to-host mapping is unit-checked (prefix traps like /created and
/settings-guide stay on www, query strings do not break matching).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/app/(main)/api/auth/google/route.ts

@@ -6,6 +6,7 @@ import {
   getCookieDomain,
   getFlowCookieOptions,
 } from '@/lib/cookieConfig';
+import { appUrl, urlForPath, wwwUrl } from '@/lib/hosts';
 import { signUserId } from '@/lib/session';
 import {
   appendRedirectParam,
@@ -40,7 +41,7 @@ export async function GET(request: NextRequest) {
       );
     }
 
-    const redirectUri = `${process.env.NEXT_PUBLIC_APP_URL}/api/auth/google`;
+    const redirectUri = appUrl('/api/auth/google');
     const scope = 'openid email profile';
     const redirectTarget = sanitizeRedirectPath(searchParams.get('redirect'));
     const oauthState = crypto.randomUUID();
@@ -72,10 +73,10 @@ export async function GET(request: NextRequest) {
   try {
     if (!state || !savedOauthState || state !== savedOauthState) {
       const invalidStateResponse = NextResponse.redirect(
-        `${process.env.NEXT_PUBLIC_APP_URL}/login?error=google-state-invalid`
+        wwwUrl('/login?error=google-state-invalid')
       );
-      invalidStateResponse.cookies.delete(GOOGLE_OAUTH_STATE_COOKIE_NAME);
-      invalidStateResponse.cookies.delete(POST_AUTH_REDIRECT_COOKIE_NAME);
+      invalidStateResponse.cookies.delete({ name: GOOGLE_OAUTH_STATE_COOKIE_NAME, path: '/', domain: getCookieDomain() });
+      invalidStateResponse.cookies.delete({ name: POST_AUTH_REDIRECT_COOKIE_NAME, path: '/', domain: getCookieDomain() });
       return invalidStateResponse;
     }
 
@@ -89,7 +90,7 @@ export async function GET(request: NextRequest) {
       );
     }
 
-    const redirectUri = `${process.env.NEXT_PUBLIC_APP_URL}/api/auth/google`;
+    const redirectUri = appUrl('/api/auth/google');
 
     // Exchange code for tokens
     const tokenResponse = await fetch('https://oauth2.googleapis.com/token', {
@@ -220,7 +221,7 @@ export async function GET(request: NextRequest) {
           authMethod: 'google',
           isNewUser: isNewUser.toString(),
         }));
-    const redirectUrl = new URL(`${process.env.NEXT_PUBLIC_APP_URL}${onboardingTarget}`);
+    const redirectUrl = new URL(urlForPath(onboardingTarget));
 
     const response = NextResponse.redirect(redirectUrl.toString());
     response.cookies.set('userId', signUserId(user.id), getAuthCookieOptions());
@@ -234,7 +235,7 @@ export async function GET(request: NextRequest) {
   } catch (error) {
     console.error('Google OAuth error:', error);
     const errorResponse = NextResponse.redirect(
-      `${process.env.NEXT_PUBLIC_APP_URL}/login?error=google-signin-failed`
+      wwwUrl('/login?error=google-signin-failed')
     );
     errorResponse.cookies.delete({ name: GOOGLE_OAUTH_STATE_COOKIE_NAME, path: '/', domain: getCookieDomain() });
     errorResponse.cookies.delete({ name: POST_AUTH_REDIRECT_COOKIE_NAME, path: '/', domain: getCookieDomain() });