fix(extensions): coerce non-mapping YAML config roots to {} in ConfigManager (#3345)

ConfigManager._load_yaml_config returned yaml.safe_load(...) or {}, which
only guards falsy roots — a truthy non-mapping root (a YAML list or
scalar) flows straight into _merge_configs, whose .items() raises
AttributeError. get_config()/has_value()/get_value() then crash, and via
should_execute_hook's blanket 'except Exception: return False' every
config-based hook condition for that extension is silently disabled.
Coerce a non-dict root to {}, mirroring the existing non-dict-root guard
in get_project_config(). Hardens all three call sites in one place.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/specify_cli/extensions/__init__.py

@@ -2688,7 +2688,12 @@ class ConfigManager:
             return {}
 
         try:
-            return yaml.safe_load(file_path.read_text(encoding="utf-8")) or {}
+            data = yaml.safe_load(file_path.read_text(encoding="utf-8"))
+            # Coerce a non-mapping root (list/scalar, or None for an empty
+            # file) to {} so callers that iterate/merge the result — e.g.
+            # _merge_configs' .items() — never crash. Mirrors the same
+            # non-dict-root guard in get_project_config().
+            return data if isinstance(data, dict) else {}
         except (yaml.YAMLError, OSError, UnicodeError):
             return {}