refactor(tasks): remove g1_flip_tracking task

[TATP-233]

Summary

• Removed the g1_flip_tracking task end to end: the G1FlipTracking / G1FlipTrackingSAC registry identities, their ppo/appo/sac owner YAMLs, the migration-matrix entries, the support-matrix generator entries, and all test and docs references.
• Why: the task is no longer a supported production profile; keeping its owners, registrations, and audit rows advertises a task that cannot be trained or played.
• No user-facing behavior change for retained tasks: x2_wall_flip_tracking, g1_box_tracking, g1_wbt_obs, and the core g1_motion_tracking paths are untouched. The generic flip CSV motion tooling in scripts/motion/ and the .gitignore entries for local flip datasets are intentionally kept.

Scope boundary: only g1_flip_tracking is removed. The zh_CN sim2sim status page keeps its remaining historical rows (the page was already a stale snapshot relative to scripts/audit_sim2sim_contracts.py; refreshing it wholesale is out of scope).

Linked Work

• Issue: none (direct maintainer request)
• Parent roadmap (when applicable): -
• Roadmap declared base (when applicable): -
• Milestone: -
• Base branch: develop/tensor-runtime

Validation

• make test-all passed on the final local head before this PR was created or updated
• Additional task-specific validation listed below

Commands actually run:

make test-all          # check + test-cov + test-benchmark-smoke: all passed (exit 0)
uv run pytest tests/tasks/test_production_registry_closeout.py tests/tasks/test_flashsac_owner_contract.py tests/config/test_g1_motion_tracking_owners.py tests/scripts/test_audit_sim2sim_contracts.py tests/scripts/test_check_docs.py -q   # 48 passed
uv run pytest tests/config/test_locomotion_params.py tests/envs/test_motion_profiles.py tests/config/test_config_system.py -q -m slow   # 10 failed, all pre-existing at HEAD (19 failed at HEAD for the same reasons: missing motrix owner YAMLs, test helper missing num_joints, box obs params drift); the 9 removed flip cases failed at HEAD too
uv run scripts/generate_support_matrix.py --write   # regenerated en/zh support matrix pages
uv run scripts/audit_sim2sim_contracts.py           # runs clean, g1_flip_tracking absent

Remote CI route:

• not scheduled; local make test-all is the test gate

Impact

• Backend impact: none (config/registry/docs only; no backend code touched)
• Platform impact: both (macOS validated locally; change is platform-neutral)
• Training effect expected: no — except that --task g1_flip_tracking no longer resolves

Artifacts

• W&B: -
• benchmark result: -
• video / screenshot: -
• ONNX / checkpoint: -

Checklist

• Added or updated tests where needed (removed obsolete coverage; retained tasks' tests updated)
• Updated docs if behavior or workflow changed (en/zh motion tracking pages, zh sim2sim status, regenerated support matrix)
• Linked the driving issue (none exists; direct maintainer request)
• Noted any follow-up work explicitly (wholesale refresh of the stale sim2sim status page is out of scope)