Fix container build workflows to checkout dispatch ref

When manually dispatching a container build with --ref, the build job
now checks out the specified commit instead of the branch HEAD. This
allows building containers from feature branches before merging.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.forgejo/workflows/build-container-nix.yaml

@@ -53,6 +53,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+        with:
+          ref: ${{ inputs.ref || github.sha }}
 
       - name: Check for default.nix
         id: check

.forgejo/workflows/build-container.yaml

@@ -54,6 +54,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
+        with:
+          ref: ${{ inputs.ref || github.sha }}
 
       - name: Check for Dockerfile
         id: check

docs/changelog.d/+fix-container-build-ref.bugfix.md

@@ -0,0 +1 @@
+Container build workflows now checkout the dispatch ref when building from feature branches, fixing "No Dockerfile — skipping" errors for containers not yet on main.

mise-tasks/container-build-and-release

@@ -5,7 +5,7 @@
 # ///
 #MISE description="Trigger container build workflows via Forgejo API"
 #USAGE arg "<container>" help="Container name (directory under containers/)"
-#USAGE flag "--ref <ref>" help="Commit SHA to build (defaults to current HEAD)"
+#USAGE flag "--ref <ref>" help="Commit SHA or branch to build (defaults to current HEAD)"
 #USAGE flag "--dry-run" help="Show what would be done without triggering"
 """Trigger container build workflows via Forgejo API dispatch.