fix(gateway,cron): reuse existing _HERMES_GATEWAY marker; tighten cron regex

Follow-up to the salvaged #30728:
- Gateway already exports _HERMES_GATEWAY=1 at startup (gateway/run.py) and
  cli.py already keys off it. Drop the redundant new HERMES_IN_GATEWAY var;
  guard stop/restart on _HERMES_GATEWAY instead. One marker for one fact.
- Drop the greedy \bgateway.*restart alternation from the cron lifecycle
  filter — it false-positived on legit prompts that merely mention an
  unrelated gateway + a restart (API/payment gateway monitoring). The
  specific 'hermes gateway (restart|stop|start)' pattern already covers the
  real command.
- Rework the two negative guard tests to sentinel the first downstream call
  so they don't drive real signal delivery (tripped the live-system guard).
- Add false-positive regression cases to test_safe_commands.

gateway/run.py

@@ -1005,10 +1005,6 @@ except Exception as _bootstrap_exc:
 # Gateway runs in quiet mode - suppress debug output and use cwd directly (no temp dirs)
 os.environ["HERMES_QUIET"] = "1"
 
-# Mark that we are inside the gateway process — used by `hermes gateway stop/restart`
-# to refuse self-targeting calls that would kill the agent's own runtime.
-os.environ["HERMES_IN_GATEWAY"] = "1"
-
 # Enable interactive exec approval for dangerous commands on messaging platforms
 os.environ["HERMES_EXEC_ASK"] = "1"