feat: add /yolo slash command to toggle dangerous command approvals (#3990)

Adds a /yolo command that toggles HERMES_YOLO_MODE at runtime, skipping
all dangerous command approval prompts for the current session. Works in
both CLI and gateway (Telegram, Discord, etc.).

- /yolo -> ON: all commands auto-approved, no confirmation prompts
- /yolo -> OFF: normal approval flow restored

The --yolo CLI flag already existed for launch-time opt-in. This adds
the ability to toggle mid-session without restarting.

Session-scoped — resets when the process ends. Uses the existing
HERMES_YOLO_MODE env var that check_all_command_guards() already
respects.

cli.py

@@ -3836,6 +3836,8 @@ class HermesCLI:
             self.console.print(f"  Status bar {state}")
         elif canonical == "verbose":
             self._toggle_verbose()
+        elif canonical == "yolo":
+            self._toggle_yolo()
         elif canonical == "reasoning":
             self._handle_reasoning_command(cmd_original)
         elif canonical == "compress":
@@ -4434,6 +4436,17 @@ class HermesCLI:
         }
         _cprint(labels.get(self.tool_progress_mode, ""))
 
+    def _toggle_yolo(self):
+        """Toggle YOLO mode — skip all dangerous command approval prompts."""
+        import os
+        current = bool(os.environ.get("HERMES_YOLO_MODE"))
+        if current:
+            os.environ.pop("HERMES_YOLO_MODE", None)
+            self.console.print("  ⚠ YOLO mode [bold red]OFF[/] — dangerous commands will require approval.")
+        else:
+            os.environ["HERMES_YOLO_MODE"] = "1"
+            self.console.print("  ⚡ YOLO mode [bold green]ON[/] — all commands auto-approved. Use with caution.")
+
     def _handle_reasoning_command(self, cmd: str):
         """Handle /reasoning — manage effort level and display toggle.