feat: support npm scoped package specifiers for plugins

Plugins can now be referenced as "@quartz-community/<name>" in
quartz.config.yaml and via 'quartz plugin add'. The npm path skips
git installation and resolves from node_modules.

Changes:
- gitLoader.ts: detect @scope/name as npm package in parsePluginSource()
- config-loader.ts: skip git install for npm packages, read manifests
  from node_modules via createRequire
- install-plugins.ts: filter npm packages from prebuild, fallback to
  YAML config parsing to avoid loading full quartz.ts
- plugin-data.js: npm detection in CLI parseGitSource()
- plugin-git-handlers.js: npm install path in handlePluginAdd()
- package.json: add missing hast-util-from-html dependency

package.json

@@ -47,6 +47,7 @@
     "esbuild-sass-plugin": "^3.6.0",
     "github-slugger": "^2.0.0",
     "globby": "^16.1.0",
+    "hast-util-from-html": "^2.0.0",
     "hast-util-to-jsx-runtime": "^2.3.6",
     "isomorphic-git": "^1.36.3",
     "lightningcss": "^1.31.1",