v0.4.0

Make the generated bootstrap deployable as-is

The snapcd root now gets a backend, a pinned provider version,
create-or-reuse switches for stack and namespace, and inputs wired
for every variable the modules need. Variables move to variables.tf,
and every generated folder gets a README with the commands to run it.

+semver: minor

## Release Notes

<!-- release-notes -->
**The generated Snap CD bootstrap can now be applied as-is.** It gets a state backend, a pinned provider version, create-or-reuse switches for the stack and namespace, and inputs wired for every variable the modules need.

**Every generated folder now includes a README** with the commands to run it. Variable declarations move from main.tf to variables.tf. Existing maps report as stale — re-run `demonolith refactor map`.
<!-- /release-notes -->