feat(tui): put every command in the wizard, not just new

[ttncode]

What this changes

A bare scaffold walked to a scaffold new command and nothing else. The two commands added since — update and publish — existed only for someone who already knew to type them, and the wizard is how a first-time user finds a command in the first place.

It now asks what to do first:

? What do you want to do?
    new (generate a project)
  » update (bring this project up to this toolbox)
    publish (create its GitHub repository and apply its settings)

update and publish both act on a project that already exists, so outside one they are not offered at all — the same reasoning docs/tour/09-wizard.md already gives for never asking a web project about a database: a refusal the user can walk into is worse than one they cannot. With one action to choose from the screen is skipped, because a menu with one answer asks nothing and costs a keystroke.

publish asks its one real question (visibility, private first, matching what the flag defaults to unset). update asks nothing — it takes only a directory, and the wizard already knows which.

Two smaller things, both while passing:

• is_scaffold_project comes out of scaffold. The same two-line check was written out three times and the wizard needed a fourth.
• The single y/N gate is now one function rather than three copies.

How it was verified

• Five pure-function tests: what the menu holds inside and outside a project, that every action carries a description, that private is offered first, and that the answer column still fits the widest question — measured from the prompts, so a new screen widens the column rather than overflowing it.
• One test asserts every action the menu offers is one scaffold's own main has a case for, so the menu and the dispatch cannot drift. This repository has shipped a second copy of a list that then drifted twice (scripts/adapter-matrix.sh exists because of the first).
• A pty test drives the real screens from inside a project, reaches scaffold publish --public, and asserts the name prompt — which belongs to new — was never shown.
• One existing pty test needed relaxing: it matched the collapsed answer line with two literal spaces, and the new prompt is one character wider, so the answer column moved. It now matches a run of spaces; it is about there being exactly one collapsed line, not about the column's width.

Checklist

• mise run lint passes
• mise run test-runner passes
• New behaviour has a test that fails without the change
• Docs that describe changed behaviour were updated in the same commit
• No unrelated changes