Bound external catalog cross-match with a hard timeout

[eagnespuerto]

Problem

Fetch & vet froze at "External catalog cross-match" and later ended with "stream timed out".

• Gaia.launch_job_async polls the ESA job queue with no time limit.
• The SIMBAD query in astroquery ≥0.4.8 runs through pyvo, which ignores TIMEOUT.
• Cross-match sends no progress events while it runs, so the SSE stream's 10-minute no-event check gives up.

Fix (backend/app/pipeline.py, mirrored in pios/vetstar_pi/pipeline.py)

• Gaia, SIMBAD and NASA Exoplanet Archive now run at the same time in a shared thread pool, with a 30 s total budget (CROSSMATCH_TIMEOUT_S). The exoplanets.org fallback gets the same budget.
• A source that runs late becomes {"error": "timed out after 30s"}, and the verdict is left as it was.
• Gaia now uses the synchronous launch_job. The query is a single-row cone search.
• The Gaia and SIMBAD queries moved into their own functions: _query_gaia_dr3 and _query_simbad.

Testing

• Stubbed a Gaia query that hangs for 60 s. With a 2 s budget, cross-match returned in 2.1 s with the SIMBAD result kept.

🤖 Generated with Claude Code

https://claude.ai/code/session_0117Lzq78TmMPd1FXyxq2SXF

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[eagnespuerto]

Backend tests: 83 passed, 1 failed. The failure, test_microlensing_coverage.py::test_all_known_windows_are_monotonic_in_start, also happens on main without this PR. It's in microlensing coverage code that this diff doesn't change, so I've left it out of this PR.

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