Generate change-log pages in Netlify preview builds

Details

The /changelog/ pages are generated at build time, but the Netlify
preview builds from netlify.toml — not the GitHub Actions workflows —
so the generator never ran and the deploy preview 404'd on /changelog/.
Unshallow Netlify's shallow clone (authenticated remote, then the
public URL, tolerating an already-full clone) and run
`npm run changelog:generate` before the Jekyll build. Verified against
a simulated depth-1 clone: the unshallow chain completes and the
generator emits all pages (650 commits → v3.2.1 on this branch).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Mn7fa3Z4bpbSAj4edBnjXA

Files changed (1)