feat: add arm64 docker & update node

[ghost]

1. Add arm64 build for Docker images
2. Run tests on non-EOL node version (20-24)
3. Add tests for Dicebear avatar v8 & v9
4. Switch to node:24-slim as base docker image for future proving
5. Update all possible dependencies (fastify@v5 has a major breaking change)

[ghost]

@FlorianKoerner could you please have a look? I plan to switch back to official Docker images instead of continuing to use my own fork, danke!

[Copilot]

Pull Request Overview

This PR enhances platform support by adding ARM64 builds, updates the Node.js version to v24 across Docker and CI, and expands dependency and test coverage for newer Dicebear avatars.

• Upgrade base Node.js image to 24-slim and adjust tests/workflows to run on Node 20, 22, and 24
• Add QEMU and Buildx steps for multi-architecture Docker image builds (amd64 & arm64)
• Update dependencies and add tests for Dicebear avatar versions 8 and 9

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/http.test.js	Expanded test matrix to include Dicebear v8 and v9 avatars
package.json	Updated Node engine range and bumped dependencies to latest minors
Dockerfile	Switched build and prod stages to use node:24-slim
.github/workflows/test.yml	Updated CI matrix to run on Node.js 20, 22, and 24
.github/workflows/docker.yml	Added QEMU/setup and Buildx for multi-arch builds, enabled arm64

[FlorianKoerner]

Thank you very much. I have added a few comments.

[FlorianKoerner]

Looks good. Thank you.