chore(booter): complete P2P/POSIX roadmap — ctx 1.48, VFS, shell, docs

- Bump bareOsCtxApiVersion to 1.48.0; sync CHANGELOG, compatibility matrix,
  syscalls.example.json, ctx d.ts, generated ctx-client helper
- POSIX: getconf _SC_NPROCESSORS_ONLN; shell set -o pipefail + BARE_OS_PIPESTATUS;
  posix_utilities schema v2 + JSON Schema; generated dashboard refresh
- Host/subprocess: bare-subprocess then Node child_process spawn; optional
  backend on ctx.bareOsTrySpawnHostSubprocess; bin-worker WASM wall budget
- VFS: BARE_OS_VFS_SYSTEM_IMAGE_WRITE for system image writes + warm-cache
  eviction path; guest /.bare/account EACCES test; environ TOKEN redaction test
- Docs: corestore snapshot non-goal in package-bare-os-booter; PEAR-RUN links
  → docs/PEAR-RUN.md; POSIX pretest matrix in scripts/README + dev guide;
  environment appendix (PIPESTATUS, WASM_MS, system image write)
- Seeder: keep kernel/ mirror in sync after bundle + coreutils builds

Verified: npm test -w bare-os-booter, npm run pretest

docs/CONTRIBUTING-DOCS.md

@@ -54,7 +54,7 @@ If a diagram would need pixel-perfect branding or screenshots, add a **placehold
 ## Links and paths
 
 - Use **relative** `.md` links between docs so [scripts/verify-doc-links.mjs](../scripts/verify-doc-links.mjs) can resolve targets.
-- The link checker walks `docs/`, `handbook/`, `developer-guide/`, `users-manual/`, `scripts/`, `packages/`, `kernel/`, plus root `README.md`, `DOCUMENTATION.md`, and `PEAR-RUN.md`.
+- The link checker walks `docs/`, `handbook/`, `developer-guide/`, `users-manual/`, `scripts/`, `packages/`, `kernel/`, plus root `README.md` and `DOCUMENTATION.md` (and any `.md` under those trees, including `docs/PEAR-RUN.md`).
 - **`packages/bare-os-seeder/kernel/**`** is skipped (mirror of `kernel/`); fix links in **`kernel/**`** only.
 
 ---