feat(chat): floating back-to-bottom button with End-key shortcut

Add a floating back-to-bottom control to the chat message list that
appears when the user scrolls up away from the live bottom. The button
auto-docks to the right edge after 15s of inactivity (with a subtle
breathing pulse) and un-docks on mouseenter, keeping it unobtrusive
while reading history.

- End key jumps to the bottom, ignored when focus is in an input,
  textarea, or contentEditable field.
- Explicit jump (button click or End) forces past the stick-to-bottom
  escape lock and clears it so sticky auto-scroll resumes following new
  content; automatic scrolls still respect the escape lock so they do
  not fight the user reading history.
- Larger thumb-reach hit area and lower placement on mobile.
- New i18n key chat.scrollToBottom (zh-CN / en-US).

mateclaw-ui/src/components/chat/MessageList.vue

@@ -88,13 +88,33 @@
         </slot>
       </div>
     </div>
+
+    <!-- Floating "back to bottom" button: appears when the user scrolls up to
+         read history, auto-docks to the edge after 15s of inactivity. -->
+    <Transition name="fade-up">
+      <div
+        v-if="!isAtBottom"
+        class="scroll-to-bottom-wrapper"
+        :class="{ docked: isButtonDocked }"
+        @mouseenter="undockButton"
+      >
+        <button
+          class="scroll-to-bottom"
+          type="button"
+          :title="$t('chat.scrollToBottom')"
+          @click="goToBottom"
+        >
+          <el-icon><ArrowDown /></el-icon>
+        </button>
+      </div>
+    </Transition>
   </div>
 </template>
 
 <script setup lang="ts">
-import { computed, watch, nextTick } from 'vue'
+import { computed, ref, watch, nextTick, onMounted, onUnmounted } from 'vue'
 import { useI18n } from 'vue-i18n'
-import { ChatDotRound, DataLine, EditPen, Monitor, Right } from '@element-plus/icons-vue'
+import { ArrowDown, ChatDotRound, DataLine, EditPen, Monitor, Right } from '@element-plus/icons-vue'
 
 const { t } = useI18n()
 import MessageBubble from './MessageBubble.vue'
@@ -166,7 +186,7 @@ const isCronHeader = (msg: Message) => {
 }
 
 // 智能滚动
-const { scrollRef, contentRef, isAtBottom, scrollToBottom } = useStickToBottom({
+const { scrollRef, contentRef, isAtBottom, escapedFromLock, scrollToBottom } = useStickToBottom({
   enabled: props.autoScroll,
   offset: 70,
   smooth: true,
@@ -185,6 +205,8 @@ watch(
   () => props.messages,
   async () => {
     await nextTick()
+    // Don't auto-scroll while the user has scrolled up to read history.
+    if (escapedFromLock.value) return
     scrollToBottom()
   },
   { deep: true }
@@ -200,6 +222,63 @@ watch(
     }
   }
 )
+
+// Explicit "jump to bottom" request (button click / End key): force past the
+// escape lock and clear it so sticky auto-scroll resumes following new content.
+function goToBottom() {
+  escapedFromLock.value = false
+  scrollToBottom({ force: true, smooth: true })
+}
+
+// ========== Back-to-bottom button: auto-dock to the edge after 15s idle ==========
+const DOCK_DELAY_MS = 15000
+let dockTimer: ReturnType<typeof setTimeout> | null = null
+const isButtonDocked = ref(false)
+
+function clearDockTimer() {
+  if (dockTimer) { clearTimeout(dockTimer); dockTimer = null }
+}
+
+function resetDockTimer() {
+  isButtonDocked.value = false
+  if (!isAtBottom.value) {
+    clearDockTimer()
+    dockTimer = setTimeout(() => { isButtonDocked.value = true }, DOCK_DELAY_MS)
+  }
+}
+
+function undockButton() {
+  isButtonDocked.value = false
+  resetDockTimer()
+}
+
+watch(isAtBottom, (atBottom) => {
+  if (atBottom) { clearDockTimer(); isButtonDocked.value = false }
+  else resetDockTimer()
+})
+
+watch(scrollRef, (el, _, onCleanup) => {
+  if (!el) return
+  el.addEventListener('scroll', resetDockTimer, { passive: true })
+  onCleanup(() => el.removeEventListener('scroll', resetDockTimer))
+})
+
+// ========== End key jumps to the bottom ==========
+function handleGlobalKeydown(e: KeyboardEvent) {
+  if (e.key !== 'End') return
+  // Only respond when focus is not in an editable field (textarea / input / contentEditable).
+  const el = document.activeElement
+  if (el && (el.tagName === 'INPUT' || el.tagName === 'TEXTAREA' || (el as HTMLElement).isContentEditable)) return
+  if (isAtBottom.value) return
+  e.preventDefault()
+  goToBottom()
+}
+
+onMounted(() => document.addEventListener('keydown', handleGlobalKeydown))
+onUnmounted(() => {
+  clearDockTimer()
+  document.removeEventListener('keydown', handleGlobalKeydown)
+})
 </script>
 
 <style scoped>
@@ -396,10 +475,88 @@ watch(
   }
 }
 
-/* 滚动提示 */
+/* Back-to-bottom floating button */
-.is-scrolling .scroll-to-bottom {
+.scroll-to-bottom-wrapper {
+  position: absolute;
+  bottom: 20%;
+  right: 0;
+  z-index: 10;
+  width: 48px;
+  height: 48px;
+  display: flex;
+  align-items: center;
+  justify-content: flex-end;
+  padding: 6px 8px;
+}
+
+.scroll-to-bottom {
+  width: 36px;
+  height: 36px;
+  border-radius: 50%;
+  border: 1px solid var(--mc-border, #e2e8f0);
+  background: var(--mc-bg-elevated, rgba(255, 255, 255, 0.92));
+  backdrop-filter: blur(6px);
+  color: var(--mc-text-secondary, #64748b);
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  font-size: 16px;
   opacity: 1;
   pointer-events: auto;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
+  transform: translateX(0);
+  transition: transform 0.35s cubic-bezier(0.4, 0, 0.2, 1),
+              opacity 0.35s ease,
+              box-shadow 0.2s ease,
+              background 0.2s ease;
+  flex-shrink: 0;
+}
+
+.scroll-to-bottom:hover {
+  background: var(--mc-panel-raised, #f1f5f9);
+  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.12);
+  transform: scale(1.08);
+  color: var(--mc-primary, #D97757);
+  border-color: var(--mc-primary, #D97757);
+}
+
+/* Click feedback: shrink slightly on press, then spring back. */
+.scroll-to-bottom:active {
+  transform: scale(0.88);
+  transition: transform 0.1s ease;
+}
+
+/* Docked to the edge: only ~8px stays visible. */
+.scroll-to-bottom-wrapper.docked .scroll-to-bottom {
+  transform: translateX(28px);
+  opacity: 0.45;
+  /* Subtle breathing pulse to remind the user the button is still there. */
+  animation: dock-breathe 3s ease-in-out infinite;
+}
+
+@keyframes dock-breathe {
+  0%, 100% { box-shadow: 0 0 0 0 rgba(217, 119, 87, 0); }
+  50%      { box-shadow: 0 0 8px 2px rgba(217, 119, 87, 0.18); }
+}
+
+/* Restore as soon as the pointer approaches. */
+.scroll-to-bottom-wrapper.docked:hover .scroll-to-bottom {
+  transform: translateX(0);
+  opacity: 1;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
+  animation: none;
+}
+
+/* Transition: fade + slide up */
+.fade-up-enter-active,
+.fade-up-leave-active {
+  transition: opacity 0.25s ease, transform 0.25s ease;
+}
+.fade-up-enter-from,
+.fade-up-leave-to {
+  opacity: 0;
+  transform: translateY(16px);
 }
 
 /* ===== 移动端适配 ===== */
@@ -416,6 +573,21 @@ watch(
     min-height: 240px;
   }
 
+  /* Mobile: larger button positioned lower for the thumb reach zone. */
+  .scroll-to-bottom-wrapper {
+    bottom: 12%;
+  }
+
+  .scroll-to-bottom {
+    width: 44px;
+    height: 44px;
+    font-size: 18px;
+  }
+
+  .scroll-to-bottom-wrapper.docked .scroll-to-bottom {
+    transform: translateX(36px); /* 44px - 8px = 36px */
+  }
+
   .welcome-screen {
     padding: 16px 10px;
   }

mateclaw-ui/src/i18n/locales/en-US.ts

@@ -224,6 +224,7 @@ export default {
     modelSaveFailed: 'Model switch was not saved — the next message may still use the previous model',
     openSessions: 'Session Admin',
     clearMessages: 'Clear Messages',
+    scrollToBottom: 'Back to bottom',
     goToModelSettings: 'Go to Model Settings',
     configModelFirst: 'Please configure a model first',
     modelUnavailable: 'Current model is unavailable',

mateclaw-ui/src/i18n/locales/zh-CN.ts

@@ -224,6 +224,7 @@ export default {
     modelSaveFailed: '模型切换未保存，下条消息可能仍走原模型',
     openSessions: '会话管理',
     clearMessages: '清空消息',
+    scrollToBottom: '回到底部',
     goToModelSettings: '前往模型设置',
     configModelFirst: '请先配置模型',
     modelUnavailable: '当前模型不可用',