feat(oneshot): add --usage-file JSON usage report to hermes -z (#59615)

* feat(oneshot): add --usage-file JSON usage report to hermes -z

Pipelines driving hermes -z (batch reviewers, cron scripts, eval
harnesses) had no way to account for per-invocation spend: the agent
computes estimated_cost_usd and full token counts internally, but
oneshot mode discards everything except the final response text.

- hermes -z PROMPT --usage-file PATH writes a JSON report after the
  run: estimated_cost_usd, cost_status/source, input/output/cache/
  reasoning/total tokens, api_calls, model, provider, session_id,
  completed, failed.
- Written even when the run fails (with a failure field) so callers
  can always account for spend; the write itself is best-effort and
  never masks the run's own outcome.
- Flag registered in both the full parser and the Termux fast path;
  added to both value-flag scan sets so profile detection stays
  correct.

Validation: 6 unit tests + live E2E (real -z run produced a report
with real OpenRouter cost + token counts).

* test: include usage_file kwarg in oneshot dispatch assertions

The two dispatch tests assert the exact kwargs dict passed to
run_oneshot; the new usage_file kwarg must appear there.

hermes_cli/_parser.py

@@ -112,6 +112,17 @@ def build_top_level_parser():
             "auto-bypassed. Intended for scripts / pipes."
         ),
     )
+    parser.add_argument(
+        "--usage-file",
+        metavar="PATH",
+        default=None,
+        help=(
+            "One-shot mode only: after the run, write a JSON usage report "
+            "(estimated cost, token counts, model, api_calls) to PATH. "
+            "The report is written even when the run fails, so pipelines "
+            "can always account for spend. No effect outside -z/--oneshot."
+        ),
+    )
     # --model / --provider are accepted at the top level so they can pair
     # with -z without needing the `chat` subcommand.  If neither -z nor a
     # subcommand consumes them, they fall through harmlessly as None.