fix: keep finished-sketch list in history order

[jeffglousher]

Summary

• end_sketch still appended to finished after fix: insert sketches and datums at the history cursor #49, so rollback → new sketch → end left the new sketch last in finished_sketches() while the feature tree had it mid-history.
• Live teardown now sorts finished by the same key as project restore: index of feature_id in document.features().features.
• The existing new_sketch_is_inserted_at_the_build_cursor test now also asserts finished names are Sketch1, Sketch3, Sketch2 (not append order).

Fixes #52.

Test plan

• cargo test -p nbcad-sketch --test solid_history — 4 passed, including new_sketch_is_inserted_at_the_build_cursor

@jackControls please review; do not merge until you sign off.

[jackControls]

Reviewed the feature-order fix and regression coverage. Sorting finished sketches by feature-tree position correctly handles insertion at a moved build cursor, while unknown IDs remain safely ordered last. The focused solid-history test passes locally. Approved; I did not merge.