fix(cron): reject id mutation + validate output paths under OUTPUT_DIR

Two defense-in-depth fixes on cron output path handling:

1. cron/jobs.py:update_job() rejects mutation of the immutable 'id' field
   (raises ValueError). Dashboard PUT /api/cron/jobs/{id} converts this to
   HTTP 400. Without this, an attacker who can reach the update endpoint
   could rename a job's id to '../escape' and move its output directory
   outside OUTPUT_DIR.

2. cron/jobs.py:_job_output_dir() validates job IDs before composing
   paths: rejects '.', '..', '/', '\\', absolute paths, and Windows drive
   prefixes. Used by save_job_output() and remove_job() so legacy unsafe
   IDs (from before this guard) fail closed rather than half-applying a
   shutil.rmtree or output write outside the sandbox.

Tests:
  - update_job rejects {'id': '../escape'} without renaming
  - remove_job(legacy '../escape' id) raises ValueError without deleting
    files outside OUTPUT_DIR or removing the job from the store
  - save_job_output rejects '..', './escape', 'nested/escape',
    absolute paths
  - dashboard PUT /api/cron/jobs/{id} with {'id': '../escape'} returns
    400, job list unchanged

Salvaged from PR #29826 by @zapabob. Simplified implementation:
- Dropped a 23-line _validate_job_output_id() helper using Path.parts
  semantics. The inline check (path separators + dot-components +
  is_absolute) is shorter and behaviorally identical.
- Dropped the secondary OUTPUT_DIR.resolve()/relative_to() check —
  redundant once we reject any path separator at the input boundary.
- Dropped the _docs/2026-05-21_cron-output-path-hardening_codex.md
  planning artifact (we don't check planning docs into the repo).

Co-authored-by: teknium1 <127238744+teknium1@users.noreply.github.com>

hermes_cli/web_server.py

@@ -2711,7 +2711,10 @@ async def update_cron_job(job_id: str, body: CronJobUpdate, profile: Optional[st
     selected = profile or _find_cron_job_profile(job_id)
     if not selected:
         raise HTTPException(status_code=404, detail="Job not found")
-    job = _call_cron_for_profile(selected, "update_job", job_id, body.updates)
+    try:
+        job = _call_cron_for_profile(selected, "update_job", job_id, body.updates)
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail=str(exc)) from exc
     if not job:
         raise HTTPException(status_code=404, detail="Job not found")
     return job
@@ -2755,7 +2758,11 @@ async def delete_cron_job(job_id: str, profile: Optional[str] = None):
     selected = profile or _find_cron_job_profile(job_id)
     if not selected:
         raise HTTPException(status_code=404, detail="Job not found")
-    if not _call_cron_for_profile(selected, "remove_job", job_id):
+    try:
+        removed = _call_cron_for_profile(selected, "remove_job", job_id)
+    except ValueError as exc:
+        raise HTTPException(status_code=400, detail=str(exc)) from exc
+    if not removed:
         raise HTTPException(status_code=404, detail="Job not found")
     return {"ok": True}