feat: keyboard shortcuts for email navigation

'/' focuses the search bar from anywhere (Layout-level listener).
j/k move focus up/down the email list in FolderView and SearchResults;
e archives the focused email, # trashes it. All shortcuts are ignored
while an input/textarea/select has focus, so typing is never hijacked.

A small hint footer in the bottom-right reminds users of the shortcuts.

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

frontend/src/components/Layout.jsx

@@ -1,5 +1,5 @@
 import { Link, Outlet, useLocation, useNavigate, useSearchParams } from 'react-router-dom';
-import { useEffect, useState, useCallback } from 'react';
+import { useEffect, useState, useCallback, useRef } from 'react';
 import { AuthApi, SyncApi, AnalyticsApi } from '../api/client.js';
 import Logo from './Logo.jsx';
 import DevBanner from './DevBanner.jsx';
@@ -129,9 +129,23 @@ export default function Layout() {
 
   const loc = useLocation();
   const navigate = useNavigate();
+  const searchInputRef = useRef(null);
 
   useEffect(() => { AuthApi.me().then(setUser).catch(() => {}); }, []);
 
+  // "/" focuses the search bar from anywhere, unless already typing in a field.
+  useEffect(() => {
+    const handler = (e) => {
+      if (e.key !== '/') return;
+      const tag = document.activeElement?.tagName;
+      if (tag === 'INPUT' || tag === 'TEXTAREA' || tag === 'SELECT') return;
+      e.preventDefault();
+      searchInputRef.current?.focus();
+    };
+    window.addEventListener('keydown', handler);
+    return () => window.removeEventListener('keydown', handler);
+  }, []);
+
   useEffect(() => {
     AnalyticsApi.sidebarCounts().then(setCounts).catch(() => {});
   }, []);
@@ -227,6 +241,7 @@ export default function Layout() {
         </nav>
         <form className="search-form" onSubmit={submitSearch}>
           <input
+            ref={searchInputRef}
             className="search-input"
             type="search"
             placeholder="Search… (from:, is:unread, has:attachment)"
@@ -322,6 +337,10 @@ export default function Layout() {
           <Outlet />
         </main>
       </div>
+
+      <div className="kbd-hint">
+        <kbd>/</kbd> search · <kbd>j</kbd>/<kbd>k</kbd> navigate · <kbd>e</kbd> archive · <kbd>#</kbd> trash
+      </div>
     </div>
   );
 }