fix: resolve 8 bugs affecting real users

- Fix KeyError 'root' in FileGrouper when merging groups with no root-level files
- Fix changelog commit parsing breaking on multiline bodies (use %x00 separator)
- Add empty choices/content checks in OpenAI, Anthropic, OpenRouter providers
- Fix config edit crash when config is empty
- Fix validate command using wrong color for 'no staged files'
- Add type check for corrupted YAML config (non-dict returns empty dict)

devgen/utils.py

@@ -246,7 +246,13 @@ def load_config() -> Dict[str, Any]:
 
     try:
         with config_path.open("r", encoding="utf-8") as f:
-            return yaml.safe_load(f) or {}
+            data = yaml.safe_load(f)
+            if not isinstance(data, dict):
+                print(
+                    f"Warning: Config at {config_path} is not a dict, using defaults."
+                )
+                return {}
+            return data
     except Exception as e:
         print(f"Warning: Failed to load config from {config_path}: {e}")
         return {}