Bug: `PackageCard` has no error handler; failed metadata loads become unhandled rejections

[mmcdermott]

Summary

`PackageCard` fires off `loadPackageMetadata(pkg).then(setData)` with no `.catch`. If the network call rejects (the underlying `readOrFetchToCache` throws when a fetch fails and there is no cached fallback), it surfaces as an unhandled promise rejection and the card stays in its initial `null` render forever.

Code pointers

• `src/components/ecosystem/PackageCard.tsx` line 10:
  ```tsx
  useEffect(() => {
  loadPackageMetadata(pkg).then(setData);
  }, [pkg]);
  if (!data) return null;
  ```
• `src/lib/loadAndCache.ts` lines 50–57 — where the throw originates:
  ```ts
  } catch (err) {
  if (data) { ... return data; }
  throw new Error(`Failed to fetch ${url} and no cached data available.`);
  }
  ```

Symptom

• Console pollution: an "Unhandled Promise Rejection: Failed to fetch ... and no cached data available." appears for any package whose first fetch fails (rate limit, network blip, etc.).
• The card silently never appears, with no user-visible error or retry affordance.

Suggested fix

Add a `.catch` that logs and falls back to a degraded `PackageWithMetadata` (everything from the YAML, with `stars/release/lastUpdated: null`), so the card still renders. Or have `loadPackageMetadata` itself absorb the error and return the same degraded shape it returns when `pkg.githubRepo` is missing.