Add bidirectional bandwidth diagnostics

[jacklv-coder]

What changed

• separate AI service latency from network bandwidth in human and Markdown reports
• add capped Cloudflare download and zero-filled upload measurements with proxy-path visibility
• add localized speed ratings and practical developer-readiness advice
• expose complete/partial download and upload details in JSON while preserving legacy top-level bandwidth semantics
• extend macOS networkQuality reporting to upload throughput
• document privacy, data limits, flags, and v0.5.0 behavior in English and Chinese

Why

Latency alone does not tell developers whether repository downloads or large AI code-context uploads will be usable through a proxy. This adds clear, bounded, non-billable measurements for both directions.

Validation

• npm test
• bash -n bin/ipcheck test/smoke.sh
• git diff --check
• final Codex CR: no remaining P1/P2 (GPT-5.6 Sol fallback because Luna was unavailable in the current environment)

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Remove bandwidth results from the --quick example

This example is introduced under $ ipcheck --quick, but --quick sets both RUN_BANDWIDTH=0 and RUN_UPLOAD=0, so it will only print skipped bandwidth entries rather than the shown 80/16 Mbps measurements and advice. This makes the primary quick-start output impossible to reproduce; use a normal invocation for this sample or omit the bandwidth section.

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