docs(adopt): add the frontend note and scan the module for CLI ids

foreign-sessions.js joins the files the no-id test scans, so the catalog lookup
stays one. The block's rules go where a frontend reader looks, in
src/web/CLAUDE.md, and the architecture note no longer calls the file surfaces
read-only, since File Viewer edit mode writes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/frontend-cli-no-id-branching.test.ts

@@ -36,6 +36,8 @@ const SCANNED_FILES = [
   // The command palette's new-session agent picker reads its agents from the
   // injected catalog; panels-ui.js carries no id branch, so keep it that way.
   'panels-ui.js',
+  // A row's mode comes from the same catalog, never from a list of ids here.
+  'foreign-sessions.js',
 ];
 
 /**