CI: single-trunk model — dev triggers on main, beta becomes RC-tag-triggered

Replaces the dev/beta branch split with one trunk (main): dev-track
builds still publish on every push, but the beta track now publishes
from a vX.Y.Z-rc.N prerelease tag instead of a separately-maintained
beta branch. Removes the branch nobody reliably kept in sync.

.forgejo/workflows/dev-bread-theme.yml

@@ -1,11 +1,11 @@
 name: dev bread-theme
 
-# Publishes a dev-track build on every push to `dev` — separate from
-# release-bread-theme.yml's tag-triggered stable releases. See
-# docs/release-channels.md for the three-track policy this is part of.
+# Publishes a dev-track build on every push to `main` (the trunk branch —
+# there is no separate `dev` branch). See docs/release-channels.md for the
+# release-track policy this is part of.
 on:
   push:
-    branches: ['dev']
+    branches: ['main']
     paths:
       - 'bread-theme/**'
       - 'Cargo.toml'
@@ -20,7 +20,7 @@ jobs:
         run: |
           set -euo pipefail
           rm -rf src && mkdir src
-          git clone --branch dev --depth 1 \
+          git clone --branch main --depth 1 \
             "https://git.breadway.dev/${GITHUB_REPOSITORY}.git" src
 
       - name: build
@@ -37,7 +37,7 @@ jobs:
           # what's already installed and bakery would correctly refuse it.
           LATEST_TAG="$(git ls-remote --tags --refs \
             "https://git.breadway.dev/${GITHUB_REPOSITORY}.git" 'v*' \
-            | awk -F/ '{print $NF}' | sed 's/^v//' | sort -V | tail -1)"
+            | awk -F/ '{print $NF}' | sed 's/^v//' | (grep -v -- '-' || true) | sort -V | tail -1)"
           if [ -n "${LATEST_TAG}" ]; then
             CUR="${LATEST_TAG}"
           else