Grid accuracy: require valid latest pivot calibration + refuse synthetic data

[jacklange22]

Summary

Per operator: a thesis-grade Aurora grid accuracy run (9-point 3×3 tracker grid) must use a real, current pivot calibration and never synthetic data.

Require a valid, latest pivot calibration (priority)

• The 0B probe tip vector now comes only from the latest pivot calibration whose summary.status == "success" (matching tool, has tip_vector_local_mm), newest-first under data/pivot_calibration/. New find_latest_valid_pivot_calibration / resolve_grid_tip_source helpers.
• Any hardcoded tip_vector_mm / tip_file and the coil-origin fallback are ignored — pivot only.
• No valid pivot ⇒ the run is refused (execute raises) and preflight shows a hard "Pivot Calibration" blocker. The chosen pivot run name + tip + RMSE are recorded in the bundle (pivot_calibration, pivot_tip_vector_mm, pivot_calibration_run) so the run is self-documenting.

Refuse synthetic data entirely

• Removed the dry-run synthetic data-generation path from the experiment and the page-side capture. The experiment always requires real captured points (raises if none) and rejects synthetic-flagged samples unconditionally (was: only when dry-run off). Preflight blocks synthetic captures unconditionally; page-side capture is live-tracker only.
• GridDefinitionConfig defaults: allow_coil_origin_fallback=False, dry_run=False. example.yaml stripped to real-data + pivot-required.

Verification (real pivot, not mocked)

• Live 3×3 = 9-point run auto-selects the repo's latest valid pivot 20260424_230515_pivot_calibration_review (tip [-1.06,-4.41,17.57]), aligns 9/9 at RMS 0.21 mm, records the provenance.
• No captures / synthetic captures / no valid pivot ⇒ all refused.
• 225 grid/critical/thesis/GUI tests pass (reworked the synthetic + tip-cal tests for the new behaviour; added pivot-required + latest-pivot + refusal coverage).

Reviewer notes

• Decisions (confirmed with operator): pivot validity = status=success only; synthetic = removed entirely; tip = pivot-only (no manual override).
• The inert dry_run / tip-vector GUI controls are left in place (harmless; ignored). A follow-up can hide them and surface the pivot status on the page.
• Scoped to grid accuracy; the concurrent two-segment-workspace edits in the tree were left out.

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