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.

hermes_cli/gateway.py

@@ -5424,7 +5424,7 @@ def _gateway_command_inner(args):
     elif subcmd == "stop":
         # Defense: refuse self-targeting gateway stop from inside the gateway.
         # Prevents agent-initiated kill loops when combined with supervisor KeepAlive.
-        if os.getenv("HERMES_IN_GATEWAY") == "1":
+        if os.getenv("_HERMES_GATEWAY") == "1":
             print_error(
                 "Refusing to stop the gateway from inside the gateway process.\n"
                 "This command was blocked to prevent restart loops.\n"
@@ -5509,7 +5509,7 @@ def _gateway_command_inner(args):
     elif subcmd == "restart":
         # Defense: refuse self-targeting gateway restart from inside the gateway.
         # Prevents agent-initiated kill loops when combined with supervisor KeepAlive.
-        if os.getenv("HERMES_IN_GATEWAY") == "1":
+        if os.getenv("_HERMES_GATEWAY") == "1":
             print_error(
                 "Refusing to restart the gateway from inside the gateway process.\n"
                 "This command was blocked to prevent restart loops.\n"