Add .github/workflows/ci.yml (Nim + gcc → make test). Keep selfhost-loop
as an optional/weekly job. Document CI layout; reformat hir_lower for fmt-check.
Add tools/selfhost_loop.sh with path-normalized C and stripped ELF
checks (bootstrap ×2). Wire GitHub Actions (manual/weekly/main paths)
outside default make test. Raise selfhost lexer maxTokens for large files.