[gbradham]

Summary

Session review measured the heatmap and time-in-zone from the centroid only. For novel-object investigation that is the wrong point: the body sits beside the object while the head investigates it.

• Right-click the Heatmap or Zones toggle to choose the keypoints: Centroid (all keypoints) (default), one keypoint, or several.
• Several keypoints: the heatmap bins their mean (e.g. head = nose + ears). A zone holds the animal when any chosen keypoint is inside it, so a nose reaching into an object's zone counts. A frame counts as dropped only when every chosen keypoint is missing.
• Applies to the zone table, the heatmap overlay and its PNG/CSV export, and the per-zone columns in the cohort export.
• Saved per keypoint set, like the Distances pairs. Names a session lacks are dropped, so a stale choice falls back to the centroid instead of blanking the zones.
• The zone table title names the choice, e.g. ZONES (2) · nose + l_ear + r_ear.

spatial.position_track / tracking_frame / zone_occupancy / occupancy_grid now accept a list of keypoint names for point. String values behave as before.

Test plan

• 11 new tests in test_spatial.py (mean position, dropped keypoints, any-inside zone rule, head-out/body-in, occupancy, heatmap)
• 5 new tests in test_analysis_window.py (default, menu, toggling, persistence, wiring to zones and heatmap)
• tests/unit/analysis, tests/unit/gui/review, tests/unit/gui/behavior: 2382 passed, 6 skipped
• ruff, black
• Try it in the app on a novel-object session