v0.3.1

Make the plugins directory configurable via structure.plugins in the config file and --plugins flag in alloy init. The plugins directory was hardcoded to plugins/ while all other managed directories were configurable.
```
# alloy.config.yaml
structure:
  content: &#34;src/content&#34;
  layouts: &#34;src/layouts&#34;
  plugins: &#34;src/plugins&#34;
```
Fix plugin file changes not being detected by the dev server watcher.
Fix nested plugin paths (e.g. tools/plugins) breaking Node runtime project root derivation.