feat(cron): per-job workdir for project-aware cron runs (#15110)

Cron jobs can now specify a per-job working directory. When set, the job
runs as if launched from that directory: AGENTS.md / CLAUDE.md /
.cursorrules from that dir are injected into the system prompt, and the
terminal / file / code-exec tools use it as their cwd (via TERMINAL_CWD).
When unset, old behaviour is preserved (no project context files, tools
use the scheduler's cwd).

Requested by @bluthcy.

## Mechanism

- cron/jobs.py: create_job / update_job accept 'workdir'; validated to
  be an absolute existing directory at create/update time.
- cron/scheduler.py run_job: if job.workdir is set, point TERMINAL_CWD
  at it and flip skip_context_files to False before building the agent.
  Restored in finally on every exit path.
- cron/scheduler.py tick: workdir jobs run sequentially (outside the
  thread pool) because TERMINAL_CWD is process-global. Workdir-less jobs
  still run in the parallel pool unchanged.
- tools/cronjob_tools.py + hermes_cli/cron.py + hermes_cli/main.py:
  expose 'workdir' via the cronjob tool and 'hermes cron create/edit
  --workdir ...'. Empty string on edit clears the field.

## Validation

- tests/cron/test_cron_workdir.py (21 tests): normalize, create, update,
  JSON round-trip via cronjob tool, tick partition (workdir jobs run on
  the main thread, not the pool), run_job env toggle + restore in finally.
- Full targeted suite (tests/cron/, test_cronjob_tools.py, test_cron.py,
  test_config_cwd_bridge.py, test_worktree.py): 314/314 passed.
- Live smoke: hermes cron create --workdir $(pwd) works; relative path
  rejected; list shows 'Workdir:'; edit --workdir '' clears.

hermes_cli/main.py

@@ -7429,6 +7429,10 @@ For more help on a command:
         "--script",
         help="Path to a Python script whose stdout is injected into the prompt each run",
     )
+    cron_create.add_argument(
+        "--workdir",
+        help="Absolute path for the job to run from. Injects AGENTS.md / CLAUDE.md / .cursorrules from that directory and uses it as the cwd for terminal/file/code_exec tools. Omit to preserve old behaviour (no project context files).",
+    )
 
     # cron edit
     cron_edit = cron_subparsers.add_parser(
@@ -7467,6 +7471,10 @@ For more help on a command:
         "--script",
         help="Path to a Python script whose stdout is injected into the prompt each run. Pass empty string to clear.",
     )
+    cron_edit.add_argument(
+        "--workdir",
+        help="Absolute path for the job to run from (injects AGENTS.md etc. and sets terminal cwd). Pass empty string to clear.",
+    )
 
     # lifecycle actions
     cron_pause = cron_subparsers.add_parser("pause", help="Pause a scheduled job")