feat(web): add OAuth callback pages and auth flow for Google/Zalo

- Add /auth/callback/google and /auth/callback/zalo pages that extract
  tokens from query params and persist them via the auth store
- Add handleOAuthCallback method to Zustand auth store
- Update middleware to allow /auth/callback/* as public routes
- Show OAuth error messages on login page when redirected back

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/middleware.ts

@@ -1,7 +1,7 @@
 import { NextResponse } from 'next/server';
 import type { NextRequest } from 'next/server';
 
-const publicPaths = ['/login', '/register', '/search'];
+const publicPaths = ['/login', '/register', '/search', '/auth/callback'];
 
 const publicExactPaths = ['/'];