fix(proxy): Reject out-of-range port numbers in proxy request

[skazantsev]

Description of Changes

Add port range validation (> 65535) before constructing the URL in
createProxyRequest. Without this, new URL() throws a TypeError for
invalid ports, causing an unhandled promise rejection and leaving the
client request hanging with no response.

Testing

• Patch applies cleanly via prepare-src.sh
• Confirmed the issue: curl /ports/99999/test triggers unhandled TypeError
• After fix: out-of-range ports are rejected before URL construction

Additional Notes

Follow-up to #269.

Backporting

Same fix applied to main, 1.1, and 1.0.

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