fix: manifest diff shows all resources as recreated (#672) (#673)

The manifests endpoint returns text/plain YAML, but fetchWithSafeDefaults
treats string responses as errors and returns the fallback value ([]).
Revert useGetReleaseManifest to use fetchWithDefaults which correctly
passes through text/plain responses.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/modal/InstallChartModal/InstallReleaseChartModal.tsx

@@ -143,7 +143,7 @@ export const InstallReleaseChartModal = ({
   } = useDiffData({
     selectedRepo,
     versionsError: versionsError as unknown as string, // TODO fix it
-    currentVerManifest: currentVerManifest as unknown as string, // TODO fix it
+    currentVerManifest: currentVerManifest ?? "",
     selectedVerData,
     chart: chartAddress,
   });