Upgrade Node.js from 20 to 22 LTS (#182)

## Summary
- Upgrade Dagger docs build image from `node:20-slim` to `node:22-slim`
- Upgrade forgejo-runner container from Node 20 to Node 22
- Fixes Quartz 4.5.2 `EBADENGINE` warning (requires Node >= 22)
- Node 20 EOL is 2026-04-30

Both builds verified locally via Dagger.

## Deployment
1. Merge this PR
2. Tag and release forgejo-runner v3.2.0: `mise run container-tag-and-release forgejo-runner v3.2.0`
3. Update RUNNER_LABELS version in `argocd/manifests/forgejo-runner/deployment.yaml` from `v3.1.0` to `v3.2.0`
4. `argocd app sync forgejo-runner`

The Dagger docs build change takes effect immediately on merge (no container release needed).

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

Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/182

containers/forgejo-runner/Dockerfile

@@ -24,7 +24,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     && rm -rf /var/lib/apt/lists/*
 
 # Install Node.js (required by actions/checkout and other JavaScript Actions)
-RUN curl -fsSL https://deb.nodesource.com/setup_20.x | bash - \
+RUN curl -fsSL https://deb.nodesource.com/setup_22.x | bash - \
     && apt-get install -y --no-install-recommends nodejs \
     && rm -rf /var/lib/apt/lists/* \
     && node --version