Add runtime E2E account ledger

runtime/README_E2E_ACCOUNTS.md

+# E2E Account Store
+
+`e2e_accounts.json` is generated by the E2E tests.
+
+The store records reusable test enterprises and their current flow state:
+
+- `certification_status=approved`: enterprise registration and SaaS certification passed.
+- `wanyouji_status=opened`: Wanyouji has been approved and opened.
+- `wanzhanggui_binding_status=bound`: this Wanyouji enterprise has been bound to a Wanzhanggui enterprise.
+- `latest_auth_key`: latest key used by the Wanyouji/Wanzhanggui authorization flow.
+
+Selection rules:
+
+- `E2E-SAAS-003` first uses `approved + not_opened`.
+- `E2E-AUTH-001` first uses `opened + not_bound`.
+- If no matching stored account exists, tests fall back to configured probe accounts without writing them into the store.