feat(cli,gateway): /new accepts optional session name argument

Allow users to start a fresh session and immediately set its title by
passing a name to /new (or /reset):

    /new Refactor auth module

Changes:
- hermes_cli/commands.py: add args_hint='[name]' to /new command
- cli.py: parse title argument in process_command(), pass to new_session()
- cli.py: new_session() accepts title=None, sets title via SessionDB
- gateway/run.py: _handle_reset_command() parses title, sets on new entry
- gateway/session.py: reset_session() accepts optional display_name
- tests: add test_new_session_with_title, test_reset_command_with_title,
  test_new_command_in_help_output

All 36 affected tests pass.

gateway/run.py

@@ -6896,6 +6896,17 @@ class GatewayRunner:
             new_entry = self.session_store.get_or_create_session(source, force_new=True)
             header = "✨ New session started!"
 
+        # Set session title if provided with /new <title>
+        _title_arg = event.get_command_args().strip()
+        if _title_arg and self._session_db and new_entry:
+            try:
+                from hermes_state import SessionDB
+                sanitized = SessionDB.sanitize_title(_title_arg)
+                if sanitized:
+                    self._session_db.set_session_title(new_entry.session_id, sanitized)
+            except Exception:
+                pass
+
         # Fire plugin on_session_reset hook (new session guaranteed to exist)
         try:
             from hermes_cli.plugins import invoke_hook as _invoke_hook