feat: Allow back button to close files modal

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

frontend/menu.html

@@ -544,7 +544,7 @@
       }
 
       const html = `
-        <div class="fixed inset-0 bg-black/50 flex items-center justify-center p-4 z-50">
+        <div id="gallery-modal" class="fixed inset-0 bg-black/50 flex items-center justify-center p-4 z-50">
           <div class="max-w-6xl w-full h-[90vh] rounded-2xl bg-white dark:bg-gray-900 border dark:border-gray-700 p-4 flex flex-col">
             <div class="flex items-center justify-between mb-2">
               <div class="text-lg font-medium">Files</div>
@@ -575,15 +575,32 @@
       const dlg = wrap.firstElementChild;
       document.body.appendChild(dlg);
 
-      const close = () => { try { dlg.remove(); } catch {} };
+      const close = () => {
+        if (location.hash === '#gallery') {
+          history.back();
+        } else {
+          try { dlg.remove(); } catch {}
+        }
+      };
       dlg.onclick = (e) => { if (e.target === e.currentTarget) close(); };
       dlg.querySelectorAll('.dlgClose').forEach(b => b.onclick = close);
+
+      if (location.hash !== '#gallery') {
+        history.pushState(null, '', '#gallery');
+      }
     }
 
     btnFilesRefresh.onclick = loadDirs;
     filesSearchQ.oninput = () => { clearTimeout(filesSearchQ._t); filesSearchQ._t = setTimeout(loadDirs, 300); };
     filesSortSel.onchange = loadDirs;
 
+    window.addEventListener('popstate', () => {
+      const galleryModal = document.querySelector('#gallery-modal');
+      if (galleryModal) {
+        galleryModal.remove();
+      }
+    });
+
     loadDirs();
   </script>
 </body>