[Chore] Fire roomote-main-build on main GHCR publishes

[roomote-roomote]

Opened on behalf of Matt Rubens. Follow up by mentioning @openmote, in the web UI, or in Slack.

What changed

After each successful GHCR publish on main, the notify-ops job now sends a repository_dispatch of type roomote-main-build to the ops repo named by ROOMOTE_OPS_REPO, with the same image_tag / sha / ref client payload shape as develop (image_tag is the immutable main-<short-sha> published for that build). Develop continues to fire roomote-develop-build.

Why this change was made

The main-channel ops receiver stays inert until the public Roomote publish workflow emits roomote-main-build. Wire the publisher side so main merges and image publishes can drive production autoship the same way develop already does for preview.

Impact

No user-facing product change. Opener of the production autoship path: successful main image publishes notify the configured ops repository when the dispatch token and ROOMOTE_OPS_REPO are set (still skipped for forks with the variable unset). Treat main merges as production releases; autoship does not pause for Postgres backups.

[roomote-roomote]

No code issues found. See task

Reviewed the notify-ops change in .github/workflows/publish-ghcr.yml. The if gate now allows both develop and main pushes, and the case "$GITHUB_REF" block selects roomote-main-build / main-<short-sha> for main and keeps roomote-develop-build / develop-<short-sha> for develop. The image_tag matches the immutable tag the prepare job already publishes for each branch (main was already a build/publish trigger before this PR), so the dispatched tag points at a real image. The defensive *) branch is unreachable given the job if, but harmless. needs: publish keeps the dispatch gated on a successful publish, and docs-only pushes stay skipped through the needs chain.

Non-blocking note: the main-/develop- image_tag string is recomputed here rather than consumed from needs.prepare.outputs.version, so the two definitions could drift if the tag format changes. This mirrors the pre-existing develop pattern, so no change required.