tools: fix CleanupSession error handling and move API key check to main

[changkun]

Summary

• CleanupSession: No longer stops iteration on error. Continues to next document/parse job on failure (best-effort cleanup). Also deletes parse jobs before their parent file.
• init() / main(): Move TENSORLAKE_API_KEY validation from init() to main() so that go test doesn't os.Exit(1) when the env var is absent (CI was failing because of this).