feat(ui): implement responsive mobile interface

- Add `relative` to nav for correct mobile dropdown positioning
- Increase hamburger button and mobile nav links to ≥44px touch targets
- Add mobile card view on files page (table hidden on small screens)
- Make bulk actions bar and pagination responsive/wrapping
- Add file type `accept` attribute and camera capture button on upload page
- Increase all interactive button/input sizes to ≥44px
- Add responsive CSS for pagination wrap and filter stacking at 480px"

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/static/styles.css

@@ -16,3 +16,23 @@ body {
     -webkit-mask-size: 100% 100%;
     mask-size: 100% 100%;
   }
+
+  /* Ensure pagination wraps properly on small screens */
+  .pagination {
+    flex-wrap: wrap;
+    gap: 0.5rem;
+  }
+  .pagination-buttons {
+    flex-wrap: wrap;
+  }
+
+  /* Ensure filter items stack on very small screens */
+  @media (max-width: 480px) {
+    .filter-group {
+      flex-direction: column;
+    }
+    .filter-item {
+      min-width: unset;
+      width: 100%;
+    }
+  }