Operator + contributor docs for the post-org-move world. None of these
files reference the legacy branch names (`beta` / old `main` meaning) —
they describe the new shape (`main` = active dev, `stable` = curated
release channel), so they're correct from the moment the rename happens.
Three additions/edits:
1. `docs/migration-to-org.md` (new) — operator-facing one-pager that the
in-app migration banner + the OLD GHCR package URLs (now 404) can
point at. Walks through the single `docker-compose.yml` edit needed.
2. `CONTRIBUTING.md` — new "Branch model" section explaining which
branch to target (`main` for features + most fixes; `stable` only
for small, surgical bugfix backports). Updates the "fork from beta"
step to "fork from main". Updates the release-process paragraph to
describe the two-channel model instead of the old beta→main promote.
3. `.github/PULL_REQUEST_TEMPLATE.md` — adds a target-branch hint at
the top of the template (HTML comment so it shows during PR
composition but doesn't render in the merged PR body).
Paul Nothaft