fix: keep recv DATA FIFO to avoid sendToSonny index error

[esrrhs]

Summary

• Revert the v0.14.0 RecvFrame optimization that promoted DATA payloads <= 4096 bytes to prioInter.
• Small chunks of the same TCP stream were jumping ahead of bulk frames, breaking per-sonny Index order and killing connections with sendToSonny index error.
• Bump version to 0.14.1. SOCKS5 UDP associate and send-side interactive priority are unchanged.

Test plan

• go test ./proxy
• Fetch a large HTTPS page (e.g. https://www.google.com/) repeatedly over SOCKS5/rudp and confirm no sendToSonny index error
• Confirm small requests still work (/generate_204, short redirects)

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