ci: tag main as :latest and beta as :beta

Replace the generic type=ref,event=branch tag (which produced :main / :beta from the branch name) with explicit raw rules so main publishes :latest and beta publishes :beta. Semver tag pushes still get :{version}, :{major.minor}, and the auto :latest from the default flavor; every build keeps its :{sha} tag for traceability.

https://claude.ai/code/session_012rsJRUue9w7sBD3J5gmKWK

Author: claude

.github/workflows/ci.yml

@@ -182,7 +182,8 @@ jobs:
         with:
           images: ${{ env.IMAGE_PREFIX }}/${{ matrix.component }}
           tags: |
-            type=ref,event=branch
+            type=raw,value=latest,enable={{is_default_branch}}
+            type=raw,value=beta,enable=${{ github.ref == 'refs/heads/beta' }}
             type=semver,pattern={{version}}
             type=semver,pattern={{major}}.{{minor}}
             type=sha,prefix=