新增 PWA 更新提示並整理 README

src/App.css

@@ -75,6 +75,59 @@
   background: linear-gradient(135deg, rgba(8, 47, 73, 0.96), rgba(10, 96, 84, 0.92));
 }
 
+.pwa-update-toast {
+  position: fixed;
+  left: 50%;
+  bottom: 18px;
+  z-index: 1200;
+  display: flex;
+  align-items: center;
+  gap: 14px;
+  width: min(560px, calc(100vw - 24px));
+  padding: 14px 16px;
+  border: 1px solid rgba(10, 51, 45, 0.16);
+  border-radius: 20px;
+  background: rgba(255, 249, 236, 0.96);
+  box-shadow:
+    0 22px 46px rgba(10, 51, 45, 0.22),
+    0 8px 18px rgba(10, 51, 45, 0.12);
+  transform: translateX(-50%);
+  backdrop-filter: blur(14px);
+}
+
+.pwa-update-copy {
+  display: grid;
+  gap: 2px;
+  min-width: 0;
+}
+
+.pwa-update-copy strong {
+  font-size: 1rem;
+  color: var(--panel-strong);
+}
+
+.pwa-update-copy span {
+  font-size: 0.88rem;
+  color: var(--panel-soft);
+}
+
+.pwa-update-button {
+  flex: 0 0 auto;
+  min-width: 96px;
+  padding: 10px 14px;
+  border: none;
+  border-radius: 999px;
+  background: linear-gradient(135deg, #0d5d53, #123f49);
+  color: #f8fff8;
+  font: inherit;
+  font-weight: 700;
+  cursor: pointer;
+}
+
+.pwa-update-button:hover {
+  filter: brightness(1.06);
+}
+
 .page-grid {
   display: grid;
   grid-template-columns: minmax(0, 0.9fr) minmax(0, 1.1fr);
@@ -1644,6 +1697,27 @@
 }
 
 @media (max-width: 720px) {
+  .pwa-update-toast {
+    gap: 10px;
+    bottom: 12px;
+    padding: 12px 12px 12px 14px;
+    border-radius: 16px;
+  }
+
+  .pwa-update-copy strong {
+    font-size: 0.92rem;
+  }
+
+  .pwa-update-copy span {
+    font-size: 0.78rem;
+  }
+
+  .pwa-update-button {
+    min-width: 84px;
+    padding: 9px 12px;
+    font-size: 0.84rem;
+  }
+
   .app-shell {
     width: min(100% - 14px, 1240px);
     padding: 14px 0 24px;