[kumo] Fix catalog schema initialization

[pranavkatariain]

Fixes initCatalog so awaiting it loads the generated catalog schemas before synchronous validation methods are used.

Previously, initCatalog called catalog.validateTree({}), but validation only reads already-loaded schemas and does not trigger the async schema import. This meant the documented setup path could still return Schemas not loaded.

This change:

• calls loadSchemas() directly from initCatalog
• keeps the existing initCatalog(catalog) API shape for compatibility
• adds regression coverage for the documented setup path
• removes the stale AGENTS.md note

Note: initCatalog currently accepts a catalog argument even though schema loading is shared module state. This PR keeps that API shape for compatibility and only fixes the documented setup flow.

Testing

• pnpm --filter @cloudflare/kumo test src/catalog/catalog.test.ts --run

• pnpm --filter @cloudflare/kumo typecheck

• git diff --check main...HEAD

• Reviews

  • bonk has reviewed the change
  • automated review not possible because: small catalog initialization fix reviewed manually

• Tests

  • Tests included/updated
  • Automated tests not possible - manual testing has been completed as follows: n/a
  • Additional testing not necessary because: n/a

[pranavkatariain]

/bonk review please