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

docs/reference/ctx-client-helper.generated.ts

@@ -7,10 +7,10 @@ export const BARE_OS_CTX_API_CLIENT_VERSION = '1.54.0' as const
 export const BARE_OS_CTX_DTS_SOURCE = 'packages/bare-os-booter/lib/bare-os-ctx.d.ts' as const
 
 /** Approximate count of `bareOs…` members in the DTS (diagnostic only; regenerate on contract edits). */
-export const BARE_OS_CTX_DTS_BAREOS_MEMBER_APPROX = 157 as const
+export const BARE_OS_CTX_DTS_BAREOS_MEMBER_APPROX = 158 as const
 
 /** Byte length of `bare-os-ctx.d.ts` when this file was generated. */
-export const BARE_OS_CTX_DTS_BYTES = 20491 as const
+export const BARE_OS_CTX_DTS_BYTES = 20549 as const
 
 /** Pointers for external client generators (OpenAPI / JSON Schema follow-ups). */
 export const BARE_OS_CTX_SCHEMA_HINT = {