fix(server): strip hop-by-hop proxy headers

[Gujiassh]

Summary

• strip hop-by-hop response headers (including those listed in Connection) from sandbox proxy responses
• keep proxy streaming response behavior unchanged otherwise

Testing

• python3 -m py_compile server/src/api/lifecycle.py

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[Pangjiping]

LGTM

[Gujiassh]

Follow-up: also honor Connection:-listed hop-by-hop headers on the request path, so any custom hop-by-hop header names are stripped before proxying. (Minimal diff; same file.)