feat: add 8 multi-subject couple poses with scene rankings (Fixes #14)

[laurentketterle-hub]

Summary

Multi-subject/couple pose pack with scene-based ranking — extends PoseGuide schema for two-person standing poses.

Closes #14

Deliverables

• Schema extension (src/poseguide/data/schema.py):

  • SubjectPose model for individual subjects in multi-person compositions
  • subjects, subject_count, and scene_rankings fields on Pose
  • rank_pose_for_scene() function for per-scene pose scoring

• 8 Couple Poses (data/poses/couple_*.json):

  1. couple_standing_side_by_side — Classic portrait (garden/outdoor)
  2. couple_embrace_face_to_face — Romantic close-up (wedding)
  3. couple_walking_hand_in_hand — Casual stroll (street/garden)
  4. couple_back_to_back — Fashion/cool (studio/street)
  5. couple_dip_kiss — Dramatic dip (wedding — scene_ranking: 1.0)
  6. couple_first_dance — Dance hold (wedding/event)
  7. couple_piggyback — Playful carry (street/casual)
  8. couple_sitting_bench — Relaxed bench (garden/street)

• Tests (tests/test_multi_subject.py):

  • Existence + validation of all 8 poses
  • Subject count consistency checks
  • Joint validity per subject
  • Scene ranking direct + tag-fallback scoring
  • 9 test cases total

• Each pose includes scene_rankings for wedding_garden, garden_path, street, and studio scenes.

[laurentketterle-hub]

/attempt 14

[laurentketterle-hub]

Friendly ping 👋 — this PR has been open for 3 days. Is there anything needed for review? Thanks!