feat: bulk actions for email lists

Select multiple rows (checkbox per row) in FolderView, SearchResults,
and the Senders email panel. A toolbar appears with mark read/unread,
star, archive, and trash, applied to the whole selection via
CleanupService.ExecuteAsync (already scoped to UserId).

Shared via useSelection hook and BulkToolbar component to avoid
duplicating selection state across the three list views.

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

frontend/src/pages/SearchResults.jsx

@@ -2,6 +2,8 @@ import { useEffect, useState, useCallback, useRef } from 'react';
 import { useSearchParams } from 'react-router-dom';
 import { SearchApi } from '../api/client.js';
 import EmailRow from '../components/EmailRow.jsx';
+import BulkToolbar from '../components/BulkToolbar.jsx';
+import useSelection from '../hooks/useSelection.js';
 
 const PAGE_SIZE = 50;
 
@@ -16,6 +18,7 @@ export default function SearchResults() {
   const [hasMore, setHasMore] = useState(true);
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState(null);
+  const { selected, toggle, clear, removeIds, selectedIds } = useSelection();
 
   useEffect(() => {
     setEmails([]);
@@ -23,7 +26,8 @@ export default function SearchResults() {
     setPage(1);
     setHasMore(true);
     setError(null);
-  }, [q]);
+    clear();
+  }, [q, clear]);
 
   const fetchPage = useCallback((p) => {
     if (!q.trim()) return;
@@ -70,6 +74,17 @@ export default function SearchResults() {
         <div className="fv-empty">No results for "{q}".</div>
       )}
 
+      <BulkToolbar
+        selectedIds={selectedIds}
+        onClear={clear}
+        onDone={(action, ids) => {
+          if (action === 'trash' || action === 'archive') {
+            setEmails((prev) => prev.filter((x) => !ids.includes(x.id)));
+            removeIds(ids);
+          }
+        }}
+      />
+
       {emails.length > 0 && (
         <table className="email-list">
           <tbody>
@@ -77,6 +92,8 @@ export default function SearchResults() {
               <EmailRow
                 key={e.id}
                 email={e}
+                selected={selected.has(e.id)}
+                onToggleSelect={toggle}
                 onRemove={(id) => setEmails((prev) => prev.filter((x) => x.id !== id))}
               />
             ))}