chore(6480): remove five Vue components nothing imports

HistoryPanel, InlineAssistPanel, NoteCard, WorkspaceNoteEditor and
WorkspaceTaskPanel had no importer, lazy import or global registration
anywhere in frontend/src. The features they served were replaced; token
sweeps kept restyling them because they match a glob. The two doc comments
that named HistoryPanel.vue now name VersionHistorySection.vue, the note
history that is live.

SearchBar.vue stays: it is the recorded home of snippet #2961 "SearchBar -
the search input recipe", and the two live search boxes are judged variants
of it. Deleting it would leave the recipe pointing at nothing.

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

frontend/src/utils/diff.ts

@@ -2,7 +2,7 @@
  * Line diff — one copy, for every surface that shows what changed.
  *
  * WHY THIS FILE EXISTS. The one LCS diff walk, shared by `useAssist.ts`,
- * `HistoryPanel.vue`, `VersionHistorySection.vue` and the rule edit history.
+ * `VersionHistorySection.vue` and the rule edit history.
  * A copy per consumer means a fix has to be found in N places by someone who
  * does not know N.
  */