fix(civitai): surface missing-model diagnostics and anchor image-page URL parsing

- Return the ResourceNotFoundError detail from get_civitai_versions and
  get_model_versions_status instead of a bare "Model not found", and let
  the download modal display the server-provided message
- Anchor extract_civitai_image_id / extractCivitaiImageId to
  ^/images/<id> so API paths and partial numeric IDs are rejected, same
  as the model-page parsing fix in #1140

py/routes/handlers/misc_handlers.py

@@ -2881,9 +2881,10 @@ class ModelLibraryHandler:
 
             try:
                 response = await metadata_provider.get_model_versions(model_id)
-            except ResourceNotFoundError:
+            except ResourceNotFoundError as exc:
                 return web.json_response(
-                    {"success": False, "error": "Model not found"}, status=404
+                    {"success": False, "error": str(exc) or "Model not found"},
+                    status=404,
                 )
             if not response or not response.get("modelVersions"):
                 return web.json_response(

py/routes/handlers/model_handlers.py

@@ -2359,8 +2359,8 @@ class ModelCivitaiHandler:
             metadata_provider = await self._metadata_provider_factory()
             try:
                 response = await metadata_provider.get_model_versions(model_id)
-            except ResourceNotFoundError:
-                return web.Response(status=404, text="Model not found")
+            except ResourceNotFoundError as exc:
+                return web.json_response({"error": str(exc)}, status=404)
             if not response or not response.get("modelVersions"):
                 return web.Response(status=404, text="Model not found")