feat(ci): build custom Docker images for Gitea Actions compatibility

- Create Dockerfile.ci-base with Bun, Node.js, and Playwright pre-installed
- Add build-ci-images workflow that triggers on package.json changes
- Update PR workflow to use custom ci-base image instead of GitHub Actions
- Update Release workflow to use custom ci-base image
- Remove dependency on oven/setup-bun@v2 GitHub Action
- Remove dependency on docker/setup-buildx-action GitHub Action
- Images are automatically built when dependencies in package.json update
- Weekly scheduled rebuild ensures tools stay current

This resolves the 'authentication required: Repository not found' error
when Gitea Actions tries to clone GitHub Actions from external repositories.

.gitea/workflows/release.yml

@@ -14,6 +14,9 @@ jobs:
     runs-on: ubuntu-latest
     # Skip if this is an auto-generated version bump commit
     if: "!contains(github.event.head_commit.message, 'chore: bump version')"
+    container:
+      image: docker.notsosm.art/euchre-camp/ci-base:latest
+      options: --user root
 
     steps:
       - name: Checkout code
@@ -63,11 +66,6 @@ jobs:
             fi
           fi
 
-      - name: Setup Bun
-        uses: oven/setup-bun@v2
-        with:
-          bun-version: latest
-
       - name: Bump version
         id: version
         run: |
@@ -109,10 +107,6 @@ jobs:
             git push origin "$TAG_NAME"
           fi
 
-      - name: Set up Docker Buildx
-        if: steps.commit.outputs.committed == 'true'
-        uses: docker/setup-buildx-action@v3
-
       - name: Build test-capable image
         if: steps.commit.outputs.committed == 'true'
         run: |