feat(12-06): expose non-secret DB name via GET /api/setup/status (gap 3)

- status returns { setupComplete, dbName } from process.env.DB_NAME (null fallback)
- only the DB name; never DB_HOST/DB_USER/DB_PASSWORD
- SetupStatusResponse carries dbName?: string | null for the PWA read-only field

apps/pwa/src/api/client.ts

@@ -537,6 +537,12 @@ export async function saveMyCredential(payload: SaveMyCredentialPayload): Promis
  */
 export interface SetupStatusResponse {
   setupComplete: boolean;
+  /**
+   * Non-secret database name (process.env.DB_NAME) surfaced for the wizard's
+   * read-only "database connection verified" referent (gap 3). Never includes
+   * DB_HOST/DB_USER/DB_PASSWORD.
+   */
+  dbName?: string | null;
 }
 
 /**