Lazy-load optional OPFS Blueprint dependencies

[ashfame]

What

Keeps saved-site metadata serialization in opfs-site-storage.ts and loads Blueprint bundle storage only when a Blueprint-backed site is read or reset. Export-only consumers avoid eagerly loading the optional Blueprint editor path without introducing a separate metadata serializer.

Why

Bundle restoration and reset support are conditional, while metadata serialization belongs with the OPFS storage implementation. This keeps the useful lazy boundary and addresses the review concern about moving metadataToStoredFormat() solely for loading behavior.

Stack

• 2 of 4
• Base: Support filtered saved-site ZIP exports #4217
• Previous: Support filtered saved-site ZIP exports #4217
• Next: Add lightweight saved-site export API #4219

Checks

• npm exec nx test playground-website
• npm exec nx lint playground-website
• npm exec nx typecheck playground-website
• npm exec nx build playground-website

[ashfame]

Optimization analysis reveals no savings, but negligibly worse:

   API startup                Raw JS      gzip JS    Requests
  ━━━━━━━━━━━━━━━━━━━━━━  ━━━━━━━━━━━  ━━━━━━━━━━━  ━━━━━━━━━━
   Eager imports           706,309 B    174,286 B           3
  ──────────────────────  ───────────  ───────────  ──────────
   Lazy imports (#4218)    706,762 B    174,293 B           3
  ──────────────────────  ───────────  ───────────  ──────────
   Lazy-loading savings       −453 B         −7 B           0

The lazy version is negligibly larger: 0.064% raw and 0.004% gzip.

The reason is Rollup’s chunk assignment:

• With eager imports, the small Blueprint-bundle storage helper is incorporated into opfs-site-storage.
• With this PR, its dynamic import resolves through the existing Blueprint Editor chunk.
• A cold Blueprint-backed read or reset then preloads nine editor-related assets totalling approximately 1.50 MB raw / 483 KB gzip. A regular ZIP export does not trigger these assets—but it did not trigger them in the eager build either.

Hence, Closing this PR. cc: @brandonpayton