fix(#411): QA-009 — fix .env.example OIDC vars and test assertion

Update .env.example to list all 4 required OIDC vars (was missing OIDC_REDIRECT_URI).
Fix test assertion to match username->email rename in signInWithCredentials.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/lib/auth-client.test.ts

@@ -96,7 +96,7 @@ describe("signInWithCredentials", (): void => {
       expect.objectContaining({
         method: "POST",
         credentials: "include",
-        body: JSON.stringify({ username: "alice", password: "password123" }),
+        body: JSON.stringify({ email: "alice", password: "password123" }),
       })
     );
   });