First version-locked BIT release.
Changes:
- Fix sliding lid rail clearance and add cross-section regression coverage.
- Apply lid frame width consistently to patterned lids.
- Set default chamfer to 0.6 mm.
- Add initial physical validation coverage and backlog follow-ups.
- Add version-locked packaging scripts; shipped starter/examples include boardgame_insert_toolkit_lib.4.0.8.scad.