v0.4.0

Breaking. The project moved and was renamed. The repository is now
aixgo-dev/code and the product is Aixgo Code. Nothing about how the agent
works changed in this release; every change below is a name.

Migrate each adopter repository in this order, because each step depends on the
one before it:

1. Rename .github/simplycubed.yml to .github/aixgo.yml, keeping its
   contents. Do the rename rather than running init on a repo with no config:
   init writes a blank starter, which would silently drop your gate:,
   engine:, attribution:, and everything else you had set. With the renamed
   file in place, re-running init keeps your values.
2. Run aixgo init --workflow --app-name <your-app> to write the new caller and
   self-test workflows under the new names.
3. Delete the old .github/workflows/simplycubed.yml caller. Nothing deletes it
   for you, and left in place it keeps firing on the same mention and label
   events: with the old variables still set you get duplicate runs for every
   command, and with the variables renamed you get a permanently failing run
   next to every real one.
4. Rename the repository variables and secrets and create the ax:* labels
   listed below.
5. Finish (or re-label and close out) any issue the agent has in flight before
   upgrading. The one-branch, one-pull-request, and one-state-label guards are
   keyed to the label prefix, so an issue mid-flight as sc:working on branch
   sc/N is invisible to a v0.4.0 run, which would start over as ax/N with a
   second pull request.

An unmigrated repo does not break; the new CLI reads .github/aixgo.yml, so it
behaves as if it has no config at all and refuses to run.

• Module path. github.com/simplycubed/code becomes
  github.com/aixgo-dev/code. Install with
  go install github.com/aixgo-dev/code/cmd/aixgo@<release-tag>.
• Binary. simplycubed becomes aixgo. Every subcommand is unchanged:
  aixgo init, aixgo preflight, aixgo command, aixgo run,
  aixgo address, aixgo version.
• Config file. .github/simplycubed.yml becomes .github/aixgo.yml.
• Workflows. The reusable workflow is
  aixgo-dev/code/.github/workflows/aixgo.yml, and init --workflow writes
  .github/workflows/aixgo.yml and .github/workflows/aixgo-selftest.yml.
• Variables and secrets. SIMPLYCUBED_GH_APP_CLIENT_ID,
  SIMPLYCUBED_GH_APP_PRIVATE_KEY, SIMPLYCUBED_AZURE_OPENAI_ENDPOINT,
  SIMPLYCUBED_AZURE_OPENAI_API_KEY, SIMPLYCUBED_GH_APP_LOGIN,
  SIMPLYCUBED_DRY_RUN, and SIMPLYCUBED_SANDBOX take the AIXGO_ prefix. A
  value read by the old name is not read at all. For the required values that
  means a run with only the old names set fails on a missing value rather than
  using a stale one. The optional flags are the sharp edge: an exported
  SIMPLYCUBED_DRY_RUN or SIMPLYCUBED_SANDBOX is silently ignored, so a
  shell that relied on the old dry-run flag performs real writes until the
  export is renamed.
• App name. The App this repository installs is aixgo-code. Adopters keep
  their own App name; appName: was already per-adopter and is untouched by the
  rename.
• Label prefix. The default labelPrefix is ax, so the lifecycle is
  ax:go, ax:queued, ax:working, ax:review, ax:blocked, ax:done.
  Adopt the new labels rather than configuring the old ones back:
  labelPrefix: sc still works for CLI-driven runs, but the caller workflow
  init writes triggers on the literal ax:go, so an Actions-driven repo set
  to sc would apply sc:go and silently start nothing.
• Scratch paths. The per-run scratch directory is .aixgo/ and the ledger
  branch is aixgo/ledger. The ledger starts fresh on the new branch; history
  from before the upgrade stays readable on the old simplycubed/ledger
  branch, which nothing writes to anymore.
• Attribution marker. Generated commits and pull requests are marked
  Aixgo Code.

Tags before v0.4.0 remain in the repository's history, but their go.mod
still declares the old module path, so they are not installable as
github.com/aixgo-dev/code. To run a pre-move release, install it from
github.com/simplycubed/code at that tag.