Create exception subclasses for fine-grained error handling:
- LimitExceededException: feature usage limit exceeded
- PackageNotFoundException: package code not found during provisioning
- FeatureNotFoundException: feature code not found during checks
- PackageSuspendedException: workspace packages suspended
Update EntitlementService:
- Add canOrFail() and canForNamespaceOrFail() throwing variants
- Replace firstOrFail() with explicit PackageNotFoundException in provisioning
- Import new exception types, remove unused ModelNotFoundException
Update docs/entitlements.md with Exception Hierarchy section, API reference
entries for new methods, and updated Best Practices examples.
Fixes#19
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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