feat(booter): POSIX/P2P roadmap — syscalls v4, mirror VFS, seeder snapshot hints

- Bump ctx API to 1.31.0; extend /proc/bare_os/syscalls.json schema 4 (fdModel, signalModel)
- Add /mirror/aux* routing for auxiliary Hyperdrives; optional BLAKE2b-keyed /bin cache (BARE_OS_VFS_BIN_CACHE_BLAKE2B)
- Wire seeder snapshotHintsJson from BARE_OS_SEED_* env; add seeder unit tests
- Shell: trap -p; docs for jobs/bg/trap; sync schemas, examples, compatibility matrix, handbook ch.9
- Coreutils: Issue 7 man option rows for cp/mv/ln/find/grep/sed/awk/tar/test/true; xcu-issue7-sweep tests
- Docs: env appendix, vault-threat-model, node-vs-bare-host-matrix, test:bare, CHANGELOG 1.31.0

scripts/README.md

@@ -259,6 +259,10 @@ Validates representative JSON under **`kernel/etc/bare-os/`** (e.g. **`boot.poli
 
 Maintainer helper for release/staging workflows (see script header for intended use).
 
+## Root `npm run test:bare`
+
+Runs **`bare-os-protocol`** tests, **`bare-os-booter`** **`test:bare`** (**`brittle-bare`** identity slice), and **`bare-os-seeder`** **`node --test`** helpers. Full workspace coverage remains **`npm test`** (includes **`brittle-node`** booter harness + coreutils).
+
 ## See also
 
 - Root [README.md](../README.md) — Pear + workspaces note