feat: mobile-first redesign (warm notebook aesthetic, thumb-zone capture bar)

- Editorial masthead (Fraunces + Spline Sans), warm paper/ink palette with
  terracotta accent, matching dark mode
- Thumb-zone composer: single capture input + round submit, optional note
  toggle, refocus after add for rapid capture
- Mobile-first CSS: 44-50px touch targets, 16px inputs (no iOS zoom),
  edge-to-edge scroll-snap list chips, safe-area insets, tap-highlight off,
  contained overscroll; desktop as min-width enhancement
- Staggered task-card entrance (reduced-motion aware), themed empty states
- Head: theme-color light/dark, Apple web-app metas, lang attr, font preconnect

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

app/pages/auth/callback.vue

@@ -17,7 +17,14 @@ onMounted(() => {
   min-height: 100dvh;
   display: grid;
   place-items: center;
-  color: #6b7280;
-  font: 500 1rem/1.4 system-ui, sans-serif;
+  background: #f4f1ea;
+  color: #837a6b;
+  font: 500 1rem/1.4 "Spline Sans", system-ui, sans-serif;
+}
+@media (prefers-color-scheme: dark) {
+  .callback {
+    background: #181410;
+    color: #9d9281;
+  }
 }
 </style>