say what this plugin is for, in the store's words

tags are how the marketplace is browsed rather than scrolled: a list of them on
the left, the plugins that carry one on the right. a closed vocabulary
(PLUGIN_TAGS in the platform) because free text becomes homelab, home-lab, Home
Lab and selfhosted inside a month, and a filter list of synonyms is worse than
no filter at all.

declared here rather than curated in the catalogue, so a plugin can say what it
is and nobody edits a table when one ships. the marketplace caches it on sync,
exactly as it already does for label and summary.

manifest.ts

@@ -21,6 +21,8 @@ export const manifest: PluginManifest = {
 
   label: 'Example',
   summary: 'The reference plugin — one route, nothing else',
+  /** exists only for someone writing a plugin. */
+  tags: ['Development'],
   icon: 'Puzzle',
   color: '#94a3b8',