Fix release note links and contributor credits

[webup]

What

• improve release notes for official releases so compare links use remote tags and fall back correctly
• show GitHub handles in contributor credits and avoid duplicate PR references in changelog items
• make install/download sections more compact with direct npm and desktop asset links
• add script-level tests for tag parsing, contributor formatting, and duplicate PR suppression

Why

The published release notes were using inconsistent compare bases, contributor names instead of GitHub handles, and duplicated PR links in some items. The install section was also more verbose than necessary.

How

• update scripts/release-notes.mjs to resolve release windows from remote tags only and improve contributor/PR formatting
• extend scripts/release-notes.test.mjs and wire it into test:cli
• update the release body template in .github/workflows/build.yml

Closes #97