fix(qa): remove dead calibration-metrics hook path (fixes #123)

[jakobtfaber]

Summary

The post-calibration pipeline hook extract_calibration_metrics was operating on a CalibrationMetrics dataclass as if it were a dict, causing an AttributeError whenever a bandpass table resolved (#123). The whole CalibrationMetricsRecord → hook_calibration_complete → ingest_calibration_metrics → update_calibration_trending path was already unused: the production QA backend now lives in dsa110_continuum.qa.calibration_quality and the dashboard uses validate_caltable_quality.

This PR deletes the dead code and makes qa/pipeline_hooks.py a minimal hook module, retaining a no-op hook_ese_detection_complete placeholder that photometry/ese_detection.py already attempts to call when ESE candidates are found.

Changes

• Replaced dsa110_continuum/qa/pipeline_hooks.py with a small module docstring and hook_ese_detection_complete(). Removed CalibrationMetricsRecord, extract_calibration_metrics, _find_caltables_for_ms, _compute_quality_score, _extract_residual_metrics, ingest_calibration_metrics, hook_calibration_complete, update_calibration_trending, and query_calibration_trending.
• Updated dsa110_continuum/qa/__init__.py to expose only hook_ese_detection_complete and removed outdated Phase 3.1 docstring references.

Verification

• make test-cloud PYTHON=/home/ubuntu/.venv-dsa110-312/bin/python passes (200 passed).
• ruff check dsa110_continuum/qa/pipeline_hooks.py dsa110_continuum/qa/__init__.py is clean.

Closes #123.