fix: allow request handlers to raise errors

[oboard]

Summary

• allow HTTP handlers and middleware/next callbacks to propagate checked errors
• catch unhandled request errors at dispatch and convert them to default/custom error responses while preserving async cancellation
• wire JS/native/mongoose request paths and regenerate package interfaces
• add white-box tests for default 500 handling, custom on_error, and locally caught errors

Tests

• moon fmt
• moon check --target native
• moon check --target js
• moon test --target native
• moon test --target js
• moon info
• moon check --target all

🤖 Generated with Claude Code