Add yq to forgejo-runner and replace sed YAML edits (#180)

## Summary
- Install yq in the forgejo-runner container image for structured YAML editing
- Replace fragile `sed` regex patterns with `yq` in `build-blumeops.yaml` and `cv-deploy.yaml` workflows

## Deployment
1. Merge this PR
2. Tag and release forgejo-runner v3.1.0: `mise run container-tag-and-release forgejo-runner v3.1.0`
3. Update runner label in `argocd/manifests/forgejo-runner/external-secret.yaml` from `v3.0.2` to `v3.1.0`
4. Sync the forgejo-runner app: `argocd app sync forgejo-runner`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/180

containers/forgejo-runner/Dockerfile

@@ -4,7 +4,7 @@
 # The host runner daemon creates containers from this image to run workflow steps.
 #
 # Build logic (container images, docs site) runs inside Dagger containers,
-# so this image only needs: git, Docker CLI, Dagger CLI, ArgoCD CLI, uv, and basic tools.
+# so this image only needs: git, Docker CLI, Dagger CLI, ArgoCD CLI, uv, yq, and basic tools.
 #
 # Usage: Configure runner with label like:
 #   docker:docker://registry.ops.eblu.me/blumeops/forgejo-runner:latest
@@ -59,6 +59,13 @@ RUN ARCH="${TARGETARCH:-$(dpkg --print-architecture)}" \
     && rm /tmp/dagger.tar.gz \
     && dagger version
 
+# Install yq (for editing YAML files in workflows)
+RUN ARCH="${TARGETARCH:-$(dpkg --print-architecture)}" \
+    && curl -fsSL -o /usr/local/bin/yq \
+    "https://github.com/mikefarah/yq/releases/latest/download/yq_linux_${ARCH}" \
+    && chmod +x /usr/local/bin/yq \
+    && yq --version
+
 # Install flyctl (for Fly.io cache purge after docs deploy)
 RUN curl -L https://fly.io/install.sh | sh \
     && mv /root/.fly/bin/flyctl /usr/local/bin/fly \