feat: add musl libc-test conformance suite, rename posix-* to os-test-*

[NathanFlurry]

Summary

• Rename posix- → os-test-**: All POSIX conformance infrastructure renamed to reflect the actual test suite name (Sortix os-test), including test runner, exclusions, CI workflow, report generator, and validator
• Add musl libc-test integration: Complete parallel infrastructure for the musl libc-test suite (MIT, Bytecode Alliance mirror) — tests kernel-level behavior (file locking, stat edge cases, socket ops) not just libc function correctness
• Shared schema: posix-exclusion-schema.ts → conformance-exclusion-schema.ts, used by both suites

libc-test results

• 75 tests compile for WASM (out of 144 total; 69 require fork/pthreads/dlopen)
• 69 pass (92.0%), 6 expected failures:
  • 4 wasm-limitation (dlopen/TLS DSOs — impossible in WASM)
  • 1 wasi-gap (statvfs)
  • 1 implementation-gap (strptime timezone)

New files

• scripts/import-libc-test.ts — fetch from Bytecode Alliance mirror
• native/wasmvm/c/Makefile — libc-test and libc-test-native targets
• packages/wasmvm/test/libc-test-conformance.test.ts — test runner
• packages/wasmvm/test/libc-test-exclusions.json — 6 exclusions
• scripts/generate-libc-test-report.ts / validate-libc-test-exclusions.ts
• .github/workflows/libc-test-conformance.yml
• docs/libc-test-conformance-report.mdx (auto-generated)

Test plan

• libc-test WASM build: 75/144 compile (fork/pthread tests expected to fail)
• libc-test conformance: 69/75 pass, 6 expected-fail with exclusions → suite green
• libc-test report generation: MDX + JSON produced correctly
• libc-test exclusion validation: all checks pass
• os-test validation: renamed scripts still work (3 exclusions, all checks pass)
• os-test report generation: works with renamed paths (3347/3350, 99.9%)
• TypeScript typecheck: clean

🤖 Generated with Claude Code