feat(cli,gateway): add /personality none and custom personality support

Closes #643

Changes:
- /personality none|default|neutral — clears system prompt overlay
- Custom personalities in config.yaml support dict format with:
  name, description, system_prompt, tone, style directives
- Backwards compatible — existing string format still works
- CLI + gateway both updated
- 18 tests covering none/default/neutral, dict format, string format,
  list display, save to config

gateway/run.py

@@ -1536,14 +1536,39 @@ class GatewayRunner:
 
         if not args:
             lines = ["🎭 **Available Personalities**\n"]
+            lines.append("• `none` — (no personality overlay)")
             for name, prompt in personalities.items():
-                preview = prompt[:50] + "..." if len(prompt) > 50 else prompt
+                if isinstance(prompt, dict):
+                    preview = prompt.get("description") or prompt.get("system_prompt", "")[:50]
+                else:
+                    preview = prompt[:50] + "..." if len(prompt) > 50 else prompt
                 lines.append(f"• `{name}` — {preview}")
             lines.append(f"\nUsage: `/personality <name>`")
             return "\n".join(lines)
 
-        if args in personalities:
-            new_prompt = personalities[args]
+        def _resolve_prompt(value):
+            if isinstance(value, dict):
+                parts = [value.get("system_prompt", "")]
+                if value.get("tone"):
+                    parts.append(f'Tone: {value["tone"]}')
+                if value.get("style"):
+                    parts.append(f'Style: {value["style"]}')
+                return "\n".join(p for p in parts if p)
+            return str(value)
+
+        if args in ("none", "default", "neutral"):
+            try:
+                if "agent" not in config or not isinstance(config.get("agent"), dict):
+                    config["agent"] = {}
+                config["agent"]["system_prompt"] = ""
+                with open(config_path, "w") as f:
+                    yaml.dump(config, f, default_flow_style=False, sort_keys=False)
+            except Exception as e:
+                return f"⚠️ Failed to save personality change: {e}"
+            self._ephemeral_system_prompt = ""
+            return "🎭 Personality cleared — using base agent behavior.\n_(takes effect on next message)_"
+        elif args in personalities:
+            new_prompt = _resolve_prompt(personalities[args])
 
             # Write to config.yaml, same pattern as CLI save_config_value.
             try:
@@ -1560,7 +1585,7 @@ class GatewayRunner:
 
             return f"🎭 Personality set to **{args}**\n_(takes effect on next message)_"
 
-        available = ", ".join(f"`{n}`" for n in personalities.keys())
+        available = "`none`, " + ", ".join(f"`{n}`" for n in personalities.keys())
         return f"Unknown personality: `{args}`\n\nAvailable: {available}"
     
     async def _handle_retry_command(self, event: MessageEvent) -> str: