fix: repair Crucible backend regressions

[jungdaesuh]

Summary

Fixes confirmed backend correctness regressions from the Crucible review on top of latest origin/develop.

Changes

• Fix QS/SLCONTOUR SVD sigma axis handling.
• Fix 2-D sinusoidal-integral denominator in both QS paths.
• Fix QS grid reconstruction conjugation.
• Restore wall loading across supported DIII-D geometry eras.
• Validate remote_dir before remote shell/rsync use.
• Preserve missing toksearch tree signals instead of silently dropping them, aligned with the latest direct tree-fetch path on develop.
• Use stable CRC-based mock RNG seeding.
• Route QS quality status through the shared contract vocabulary.

Tests

• uv run ruff format . -> 59 files left unchanged
• uv run ruff check . -> passed
• uv run ruff format --check . -> 59 files already formatted
• uv run ty check src -> passed
• uv run --extra service pytest -q -> 320 passed, 5 skipped

Risk

Medium: touches numerical/data-fetch paths, but each confirmed regression has focused coverage.

Rollback

Revert this PR. No migrations, data writes, or schema changes.