fix(gateway): bridge quick commands into GatewayConfig runtime

Follow-up on salvaged PR #975.

Bridge quick_commands from config.yaml into load_gateway_config(),
normalize non-dict quick command config at runtime, and add coverage
for GatewayConfig round-trips plus config.yaml bridging. This makes the
GatewayConfig quick-command fix complete for the real user-facing config
path implicated by issue #973.

gateway/run.py

@@ -1017,6 +1017,8 @@ class GatewayRunner:
                 quick_commands = self.config.get("quick_commands", {}) or {}
             else:
                 quick_commands = getattr(self.config, "quick_commands", {}) or {}
+            if not isinstance(quick_commands, dict):
+                quick_commands = {}
             if command in quick_commands:
                 qcmd = quick_commands[command]
                 if qcmd.get("type") == "exec":