The MDX content was flipped to Hexclave in PR 1481, but the URL slug
itself (/guides/other/tutorials/build-a-saas-with-stack-auth) was still
public-facing. Rename the file and update the five internal links:
- docs.json navigation reference
- 3 in-MDX cross-links in build-a-team-based-app.mdx
- 2 in-MDX cross-links in ship-production-ready-auth.mdx
Rebased onto dev after PR 1475 (cl/hexclave-pr1) was squash-merged.
Squashes the original 46-commit branch (including PR1-duplicate commits
that arrived via cherry-picks/merges) into a single commit containing
only PR2's net delta over dev.
Original PR 1481 head: 94872de407873a1cabd4085deb21b69afe8d7699
(kept locally at backup/cl-romantic-mendel-5a2c25-pre-rebase)
