fix(ci): the release step tolerates a release that already exists

A re-fired tag hits the release POST with a 409 and curl -sf turns
"already exists" into a red job while the image jobs succeed — observed
on boilerroom's v0.1.0 re-fires tonight; this workflow fails the same
way. Check-then-create makes the step idempotent.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -10,12 +10,20 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Create Gitea Release
+        # Idempotent: a re-fired tag finds its release already present and
+        # says so instead of failing on the 409.
         run: |
+          api="${{ github.server_url }}/api/v1/repos/${{ github.repository }}/releases"
+          auth='Authorization: token ${{ secrets.GITHUB_TOKEN }}'
+          if curl -sf -H "$auth" "$api/tags/${{ github.ref_name }}" > /dev/null; then
+            echo "release for ${{ github.ref_name }} already exists — nothing to do"
+            exit 0
+          fi
           curl -sf -X POST \
-            -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" \
+            -H "$auth" \
             -H "Content-Type: application/json" \
             -d '{"tag_name": "${{ github.ref_name }}", "name": "Release ${{ github.ref_name }}", "body": "Automated release for ${{ github.ref_name }}"}' \
-            "${{ github.server_url }}/api/v1/repos/${{ github.repository }}/releases"
+            "$api"
 
   build:
     runs-on: ubuntu-latest