fix(config): isolate plugin list reads from a broken JSONC layer

Plugin listing still called readConfigFile per layer, so one unparseable
project file made GET /api/config/plugins and VS Code listPluginEntries
fail. Reuse readConfigLayer isolation and pin comment-only empty parse
in the VS Code suite.

Co-authored-by: serkraser <serkraser@gmail.com>

packages/web/server/lib/opencode/shared.js

@@ -644,6 +644,7 @@ export {
   parseMdFile,
   writeMdFile,
   readConfigFile,
+  readConfigLayer,
   isPlainObject,
   readConfigLayers,
   readConfig,