Ship the QUALITY_PLAN stretch from ownership through ecosystem: C.1
lifetime elision (bootstrap + selfhost), bux fmt/test/doc CI hooks,
stdlib goldens, package registry (bux search/add), and LSP 0.4
position-sensitive locals with inferred let types. Full-tree format
pass plus Map/Set remove double-free fix.
- Add lib/Slice.bux with Slice<T> generic struct
- Fix C backend to recognize Slice/Slice* as generic types
- Use var instead of let for uninitialized Slice<T> locals
- Selfhost loop passes, tests pass