Unpin Bun 1.4.3 installs once a release after 1.4.4 fixes the Linux install panic #4161

Follow-up from #2506. As of 2026-11-09, Bun 1.4.4's isolated bun install still panics on Linux (index out of bounds ... index is 4294967295), and 1.4.4 is still the latest release. The workaround in the PR for #2506 installs on 1.4.3 and compiles on 1.4.4: in the box's Dockerfile deps stage and desktop-drop's build job.

When a Bun release after 1.4.4 ships:

1. Move every CI pin (bun-version / BUN_VERSION, still 1.4.3) to it: sed -i '' -E 's/(bun-version|BUN_VERSION): "1\.4\.[34]"/\1: "X.Y.Z"/' .github/workflows/*.yml, plus the minimum in MAC_SETUP.md.
2. Remove the extra setup-bun step from desktop-drop's build job, and put the box Dockerfile back on a single image (by digest).
3. Check that the Linux jobs get past bun install.

If the new release still panics, send Bun a minimal repro. That is Bun's repo, so check with the owner first.