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

tests/routes/test_misc_routes.py

@@ -37,6 +37,7 @@ from py.utils.session_logging import (
 )
 from py.routes.misc_route_registrar import MISC_ROUTE_DEFINITIONS, MiscRouteRegistrar
 from py.routes.misc_routes import MiscRoutes
+from py.services.errors import ResourceNotFoundError
 
 
 def _json_payload(response) -> dict[str, Any]:
@@ -2748,6 +2749,38 @@ async def test_get_model_versions_status_supported_type_stays_interactive():
     ]
 
 
+@pytest.mark.asyncio
+async def test_get_model_versions_status_surfaces_not_found_details():
+    """A missing CivitAI model keeps the provider's diagnostic message."""
+
+    class NotFoundProvider:
+        async def get_model_versions(self, _model_id):
+            raise ResourceNotFoundError("Civitai model 3390681 was not found")
+
+    async def metadata_factory():
+        return NotFoundProvider()
+
+    handler = ModelLibraryHandler(
+        ServiceRegistryAdapter(
+            get_lora_scanner=fake_scanner_factory,
+            get_checkpoint_scanner=fake_scanner_factory,
+            get_embedding_scanner=fake_scanner_factory,
+            get_other_scanner=fake_scanner_factory,
+            get_downloaded_version_history_service=fake_download_history_service_factory,
+        ),
+        metadata_provider_factory=metadata_factory,
+    )
+
+    response = await handler.get_model_versions_status(
+        FakeRequest(query={"modelId": "3390681"})  # pyright: ignore[reportArgumentType]
+    )
+    payload = _json_payload(response)
+
+    assert response.status == 404
+    assert payload["success"] is False
+    assert "3390681" in payload["error"]
+
+
 class DummySidecarMigrationUseCase:
     def __init__(self, result):
         self.result = result