Horizontal patient cards, dark scrollbar, functional input controls

- globals.css: thin dark-themed scrollbar (Firefox + WebKit) so scroll
  areas no longer show the white default; `no-scrollbar` regions still win.
- patient-cards.tsx: render the cards in a horizontal scroll row (each
  w-80 shrink-0 snap-start), loading skeletons included.
- chat-input.tsx: wire the controls — Attach opens a file picker with
  removable chips; Access / response mode / specialty / facility / time
  range are real DropdownMenu radio selectors (via a SelectPill helper)
  that remember the choice. Mic stays visual-only for now. Layout/styling
  unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/app/globals.css

@@ -121,6 +121,22 @@
 @layer base {
   * {
     @apply border-border outline-ring/50;
+    scrollbar-width: thin;
+    scrollbar-color: oklch(1 0 0 / 18%) transparent;
+  }
+  *::-webkit-scrollbar {
+    width: 8px;
+    height: 8px;
+  }
+  *::-webkit-scrollbar-track {
+    background: transparent;
+  }
+  *::-webkit-scrollbar-thumb {
+    background-color: oklch(1 0 0 / 18%);
+    border-radius: 9999px;
+  }
+  *::-webkit-scrollbar-thumb:hover {
+    background-color: oklch(1 0 0 / 28%);
   }
   body {
     @apply bg-background text-foreground;