Detect ZIP archives as binary content

[officialasishkumar]

Summary

• keep the existing content_inspector path and add a narrow ZIP magic fallback when it would otherwise classify archive bytes as UTF-8 text
• treat the standard ZIP signatures (PK\x03\x04, PK\x05\x06, PK\x07\x08) as binary content
• add unit and integration regressions covering ZIP detection without changing other PK-prefixed text

Testing

• cargo test --lib
• cargo test --test integration_tests

Closes #3663

[keith-hall]

Nice, thanks!