feat: add HAProxy and FlowProxy config to BuilderHub and forward HAProxy ports from buildernet VM

[fkondej]

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[claude]

Claude finished @fkondej's task in 1m 21s —— View job

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PR Review: #376

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• Analyze changes and identify issues
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Summary: This PR adds two things: (1) FlowProxy and HAProxy configuration sections to the BuilderHub config YAML, and (2) HAProxy port forwarding (HTTP 10080→80, HTTPS 10443→443) for the buildernet QEMU VM.

The changes are clean and follow existing patterns in both files. No significant issues found.

Minor observations:

• The HAProxy rate limit values are quoted as strings (e.g., "1000") while the FlowProxy config uses unquoted values for addresses/ports. This is likely fine if the consumer expects strings for rate limits, but worth confirming consistency with the upstream config schema.
• The rate limits are set very high (e.g., 10GB bytes-in rate for regular, 100GB for privileged), which makes sense for a local playground/dev environment to avoid interfering with testing.
• The flashbots_orderflow_signing_address is set to the zero address — appropriate for a playground config where no real signing is needed.

No blocking issues. LGTM.