docs: replace dead payment points links

[xt1085]

Summary

• Replace the unavailable Suredbits Point Time Lock Contracts reference in RFC-0241 and RFC-0310.
• Point both links to the same article hosted on the original author's website.
• Preserve the link text and all surrounding RFC wording.

Verification

• bash scripts/build.sh
• export PATH="$PWD/.build-tools:$PATH" && mdbook test
• Confirmed the old URL is absent from the rendered book.
• Confirmed both target pages render the replacement URL with the original link text.
• Confirmed the replacement returns HTTP 200 and the old URL returns HTTP 522.

Both canonical commands were run on x86_64 because the repository build script downloads x86_64 mdBook binaries.

Note

git diff --check reports a trailing space on the changed RFC-0310 line. That space already exists in the baseline line and was deliberately preserved so this patch changes only the URL destination.

Closes #151