feat(ui): add discussions and semantic theming

Generate web discussion snapshots in CI; native builds use the public
feed and an offline cache.

index.html

@@ -46,6 +46,7 @@
          file) so CAD text renders non-Latin scripts on the web. (#141) -->
     <link data-trunk rel="copy-dir" href="web/fonts" />
     <link data-trunk rel="copy-file" href="web/ocs-parse-worker.js" />
+    <link data-trunk rel="copy-file" href="web/discussions.json" />
   </head>
   <body>
     <div id="loading">