feat(chat): implement pull-to-refresh functionality and pagination for chat history

src/app/chat/components/chat-area.module.css

@@ -1,9 +1,13 @@
 /* ChatArea 消息列表样式 */
 
 .area {
+  --chat-pull-offset: 0px;
+
+  position: relative;
   flex: 1 1 auto;
   min-height: 0;
   overflow-y: auto;
+  overscroll-behavior-y: contain;
   padding:
     var(--spacing-lg, 16px)
     calc(var(--chat-inline-padding, 20px) + var(--app-safe-right, 0px))
@@ -11,11 +15,49 @@
     calc(var(--chat-inline-padding, 20px) + var(--app-safe-left, 0px));
 }
 
+.pullIndicator {
+  position: absolute;
+  top: var(--spacing-sm, 8px);
+  left: 50%;
+  z-index: 2;
+  display: inline-flex;
+  min-height: 34px;
+  align-items: center;
+  gap: 7px;
+  padding: 0 12px;
+  border: 1px solid rgba(255, 255, 255, 0.16);
+  border-radius: 999px;
+  background: rgba(24, 20, 30, 0.86);
+  color: rgba(255, 255, 255, 0.9);
+  font-size: var(--responsive-caption, var(--font-size-sm, 12px));
+  font-weight: 700;
+  opacity: 1;
+  pointer-events: none;
+  transform: translate(-50%, calc(var(--chat-pull-offset) - 42px));
+  white-space: nowrap;
+  box-shadow: 0 8px 22px rgba(0, 0, 0, 0.28);
+}
+
+.pullIndicator[aria-hidden="true"] {
+  opacity: 0;
+}
+
+.pullIndicator svg[data-spinning="true"] {
+  animation: pullIndicatorSpin 0.8s linear infinite;
+}
+
 .content {
   display: flex;
   flex-direction: column;
   gap: var(--spacing-3, 12px);
   min-width: 0;
+  transform: translateY(var(--chat-pull-offset));
+  transition: transform 180ms ease;
+  will-change: transform;
+}
+
+.area[data-pulling="true"] .content {
+  transition: none;
 }
 
 .dateHeader {
@@ -143,3 +185,9 @@
   0%, 60%, 100% { opacity: 0.2; }
   30% { opacity: 1; }
 }
+
+@keyframes pullIndicatorSpin {
+  to {
+    transform: rotate(360deg);
+  }
+}