feat: sync compact_columns with the cortex registry

[monazhu]

Closes DS-1046 — https://linear.app/cognitive3d/issue/DS-1046

Mirrors CognitiveVR/cognitive3dpy#34 (DS-1045), which lands the same guard on the Python package.

Problem

compact_columns (R/sessions.R) is a hand-curated list copied from the Python package. This repo has no schema-sync machinery, so it drifts from the cortex field registry with nothing to catch it. The drift turned out to be larger than the ticket recorded: ten entries name keys the registry marks deprecated: true, not two. Eight of them were retired from the Python compact list some time ago and never mirrored here.

Changes

• R/registry.R records the registry keys flagged deprecated or sunsetted, with helpers that convert them to cleaned column names. The lists are hand-maintained and dated, since there is no sync script — yaml moves into Suggests so the suite can verify them against the registry itself.
• compact_columns goes from 57 to 47 columns. Removed: app_performance, immersion_score, orientation_score, ergonomics_score, boundary_score, controller_events_score, controller_engagement_score, dynamic_engagement_score, battery_efficiency, standing_percentage. Added c3d_metric_components_posture_standing_percentage, which replaced standing_percentage upstream — new sessions carry only the posture trio, and the same-named StarRocks column is a melder compatibility alias rather than a contract.
• c3d_metrics_average_fps stays. Melder intends to delete the emission but the org dashboard tile still reads it, so the registry deliberately keeps it active; noted inline.
• tests/testthat/test-compact-columns.R fails on duplicates or on any compact column the registry has deprecated or sunsetted, with lifecycle_exceptions as the escape hatch for a documented retention. A fourth test cross-checks R/registry.R against slicer_fields.yaml so the hand-maintained lists cannot silently go stale — it skips when no cvr-cortex checkout is present, which is the case in CI.
• test-sessions.R read controller_engagement_score out of compact output and would have gone red; it now reads it from full mode, and a new test asserts the dropped columns still come back with compact = FALSE.

Verification

• testthat::test_local() → 417 passed, 0 failed, 0 skipped across 7 files
• Registry cross-check ran locally against the real slicer_fields.yaml and matched both lists exactly
• Guard confirmed non-vacuous: injecting c3d_metrics_immersion_score into the list produces FAIL 1 with the intended message

Note for reviewers

This is the user-visible half of the change: default compact output loses ten columns. All of that data is still returned by compact = FALSE. Unlike the Python package, this one has no deprecation-warning machinery, so dropped columns disappear silently rather than warning first — worth deciding whether that is acceptable or whether a warning layer should follow.

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