Workspace note editor: toolbar, link suggestions, wikilink button, Ctrl+S

- Add MarkdownToolbar to the workspace note editor (was missing entirely)
- Add [[ button to MarkdownToolbar so wikilinks are discoverable in all editors;
  clicking inserts [[ which immediately triggers the WikilinkSuggestion dropdown
- Add link suggestions strip: polls /api/notes/link-suggestions 2.5s after edit,
  shows unlinked note-title mentions as clickable chips to wrap in [[...]], plus
  "All" button to apply everything at once — directly addresses the heading→wikilink
  workflow (note title appearing as heading text gets detected and offered for linking)
- Add Ctrl+S keyboard shortcut on title input and editor area to save
- Replace ✕ delete icon on note list items with trash can SVG (consistency with task panel)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/MarkdownToolbar.vue

@@ -73,6 +73,12 @@ const buttons = [
     command: () => props.editor?.chain().focus().toggleCodeBlock().run(),
     isActive: () => props.editor?.isActive("codeBlock") ?? false,
   },
+  {
+    label: "[[",
+    title: "Insert wikilink (type note title to search)",
+    command: () => props.editor?.chain().focus().insertContent("[[").run(),
+    isActive: () => false,
+  },
 ];
 </script>