feat(shell): job-aware kill, disown, jobs/set flags, fallback REPL history

- Document interactive shell vs /bin/sh in bare-os-shell man, handbook §9,
  kill(1), and shell-completion guide
- Resolve kill %n and %% to synthetic PIDs via shellBackgroundJobs
- Add disown builtin; jobs -p (pgid-only) and -l (pid column); set -o/+o to
  print errexit/nounset/pipefail/noglob
- Expand completion-engine fallback flags for common utilities
- Persist lines to /.bare/repl_history_<USER> when BARE_OS_REPL_HISTORY=1
  and Fish REPL is off (repl-session + cli-readline)
- Tests: kill job specs, set -o output, jobs -p

kernel/etc/bare-os/posix_utilities.json

@@ -1,7 +1,7 @@
 {
   "schema": 2,
   "profileId": "bare-os-posix-like",
-  "generatedAt": "2026-04-09T23:26:09.246Z",
+  "generatedAt": "2026-04-21T21:25:44.827Z",
   "note": "Sparse POSIX Issue 7 coverage hints for /bin utilities. Omitted command names are not yet profiled here.",
   "commandIndex": [
     {
@@ -444,10 +444,18 @@
       "name": "sha1sum",
       "tier": "tier1_bin"
     },
+    {
+      "name": "sha224sum",
+      "tier": "tier1_bin"
+    },
     {
       "name": "sha256sum",
       "tier": "tier1_bin"
     },
+    {
+      "name": "sha384sum",
+      "tier": "tier1_bin"
+    },
     {
       "name": "sha512sum",
       "tier": "tier1_bin"