Add missing save_config() to config.py (was imported by server.py but never pushed)

src/system/config.py

@@ -87,4 +87,20 @@ def _deep_merge(base: dict, overrides: dict) -> None:
         if key in base and isinstance(base[key], dict) and isinstance(val, dict):
             _deep_merge(base[key], val)
         else:
-            base[key] = val
+            base[key] = val
+
+
+def save_config(cfg: dict, path: Path = DEFAULT_CONFIG_PATH) -> bool:
+    """Save config dict to YAML file (preserves existing keys, overwrites in-memory state).
+
+    Returns True on success, False on failure.
+    """
+    try:
+        import yaml
+        with open(path, "w") as f:
+            yaml.dump(cfg, f, default_flow_style=False)
+        logger.info("Saved config to %s", path)
+        return True
+    except (ImportError, OSError) as e:
+        logger.warning("Failed to save config to %s: %s", path, e)
+        return False