fix(event-handler): preserve binary Web Response bodies

[svozza]

Summary

Returning a Web Response with PDF, ZIP, or octet-stream bytes could silently corrupt the body by decoding it as UTF-8. These content types now use base64 serialization, preserving the original bytes across REST API, HTTP API, and ALB responses.

Changes

• Recognize application/pdf, application/zip, and application/octet-stream as binary content types, including mixed-case values and parameters.
• Add byte-preservation regressions across all three integrations and controls for text, JSON, and XML responses.
• Document automatic encoding for Web responses and the explicit flag for other binary content types.
• Validate workspace test types, staged-file linting, and the unit suite with 100% coverage.

Issue number: closes #5698

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