v0.1: Tutorials 3 & 4 — finish or defer #53

Part of the v0.1 epic (#46).

Tutorials 3 (collaboration/PRs) and 4 (local customisation) are outline-only. Decide and execute:

• Finish them for v0.1, or clearly label as WIP/coming-soon and defer to v0.2
• Also: tutorial 2's full version still shows the old Vercel dashboard flow in places — align with current Flowershow Cloud flow