fix(sql): return error for unsupported dialect

[fallintoplace]

Summary

• Changed SQL catalog dialect resolution to return typed errors instead of panicking for unsupported dialects.
• Updated registry usage to rely on clean error flow from 'sql.NewCatalog'.
• Added test for direct catalog creation via NewCatalog with unsupported dialect.

Testing

• go test ./catalog/sql -run 'TestInvalidDialect|TestNewCatalogInvalidDialect' -count=1
• go test ./catalog/sql -count=1

[zeroshade]

LGTM. Replacing the unsupported-dialect panic with a proper error return is the right call, the supported dialect set is preserved, and both the loader and direct-constructor paths are covered by tests.