docs: replace deprecated PingCAP domains

[wuhuizuo]

Summary

• replace deprecated download.pingcap.org references with download.pingcap.com
• replace deprecated charts.pingcap.org references with charts.pingcap.com
• keep existing paths and protocols unchanged

Validation

• git diff --check
• verified no remaining download.pingcap.org / charts.pingcap.org references in the patched branch

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[gemini-code-assist]

Code Review

This pull request updates the download URL domain from .org to .com in scripts/upload.py. A suggestion was made to define the URL format string as a constant to improve code maintainability.

[gemini-code-assist]

To improve maintainability, it's better to define this hardcoded URL format string as a constant. This makes it easier to manage if the URL needs to be changed again in the future.

For example, you could add DOWNLOAD_URL_FORMAT = "https://download.pingcap.com/{}" near the other constants at the top of the file, and then change this line to:

print(DOWNLOAD_URL_FORMAT.format(remote_name))