audit(spark-B): test coverage — 11 new tests across models/proxy/i18n/gen-docs + idempotency fix

- New test/models.test.js: Opus 4.7 alias resolution, case/dot/dash variants, bare variants
- New test/account-add-proxy-ordering.test.js +3: valid public proxy flow, api_key+token coexistence, non-ERR_* error path
- New test/check-i18n.test.js: clean exit-0 + dirty exit-1 regression
- New test/gen-docs-models.test.js: HTML parses, idempotent rerun, unknown provider doesn't crash
- Fix scripts/gen-docs-models.js: line-based replace for true idempotency
- 338/338 tests pass