fix(docker): 2-stage build, apt cache mounts, .dockerignore

[McCio]

I noticed rebuilds were slow since npm install and plugin install shared a layer, so changing one busted the other. Pulling the image was also slow as everything was bundled together.

I initially split into three stages (builder, plugins, runtime) to cache npm and plugin install independently, then revised to two stages after realising that plugins with requiresInstall add native deps to root node_modules, so copying node_modules from a stage that skipped plugin install would silently drop those.

The builder stage now runs both npm ci and plugin install, each as its own layer, so the npm cache still survives a plugin-only change. The runtime stage copies node_modules and .quartz from builder.

I also added ENV NPM_CONFIG_USERCONFIG=/usr/src/app/.npmrc since plugin install can spawn child npm processes inside .quartz/plugins/<name>/, which would miss the root .npmrc otherwise, plus apt cache mounts to keep the apt cache out of the layers, a .dockerignore to keep node_modules and .quartz out of the build context, and glob patterns on quartz.lock.json and quartz.config.yaml.

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[McCio]

@saberzero1 I see you are working on main branch on the dockerfile. should I realign this? I really think this should be merged, among the other things it reduced the final image size to just ~500MB instead of ~1.5GB