feat: 登录注册表单体验优化、工作台滚动按钮交互增强、主题层视觉精修

ProfilePage.tsx（登录/注册表单优化）：
- 新增邮箱格式、手机号、密码强度前端校验逻辑
- 输入框内联校验提示（CheckCircleFilled图标+绿色文字）
- 登录态展示区增加平台能力Stats（Studio/Assets/Team）
- 表单增加kicker标签区分"账户登录"/"新用户注册"
- 手机验证码tab标签精简为"手机"

WorkbenchPage.tsx（工作台滚动交互增强）：
- 新增滚动操作按钮显隐状态管理（scrollActionsVisible/direction）
- 滚动时自动展示上下滚动按钮，950ms后自动隐藏
- scrollMessagesToLatest触发时间接展示滚动按钮
- 组件卸载时清理定时器避免内存泄漏

dark-green.css（主题层视觉精修）：
- 工作台激活态页面背景增加微光渐变和径向光晕
- 消息表面区域增加内边距和scrollbar-gutter稳定布局
- 消息列表最大宽度约束为1040px，左右padding自适应
- 消息气泡增加边框、背景、阴影层次感
- AI助手气泡与用户气泡差异化背景色
- 头像增加微边框和accent色区分
- 作者标签字号和颜色精细调整

src/features/workbench/WorkbenchPage.tsx

@@ -236,6 +236,7 @@ function WorkbenchPage({
   const keepaliveTasksRef = useRef<Record<string, WorkbenchKeepaliveTask>>(readStoredKeepaliveTasks());
   const taskAbortControllersRef = useRef<Map<string, AbortController>>(new Map());
   const lastScrollTopRef = useRef(0);
+  const scrollActionsHideTimerRef = useRef<number | null>(null);
   const shouldFollowNewMessagesRef = useRef(true);
   const pendingScrollToLatestRef = useRef(true);
   const renderedMessageIdsRef = useRef<string[]>([]);
@@ -273,6 +274,8 @@ function WorkbenchPage({
   const [promptSelectionRange, setPromptSelectionRange] = useState({ start: 0, end: 0 });
   const [mentionActiveIndex, setMentionActiveIndex] = useState(0);
   const [composerHidden, setComposerHidden] = useState(false);
+  const [scrollActionsVisible, setScrollActionsVisible] = useState(false);
+  const [scrollActionDirection, setScrollActionDirection] = useState<"top" | "bottom" | null>(null);
   const [workspaceStarted, setWorkspaceStarted] = useState(false);
 
   useEffect(() => {
@@ -441,6 +444,27 @@ function WorkbenchPage({
     "--accent-glow": `0 0 24px rgba(${accentRgb}, 0.22)`,
   } as CSSProperties;
 
+  const revealScrollActionsTemporarily = useCallback((direction: "top" | "bottom") => {
+    setScrollActionDirection(direction);
+    setScrollActionsVisible(true);
+    if (scrollActionsHideTimerRef.current !== null) {
+      window.clearTimeout(scrollActionsHideTimerRef.current);
+    }
+    scrollActionsHideTimerRef.current = window.setTimeout(() => {
+      setScrollActionsVisible(false);
+      setScrollActionDirection(null);
+      scrollActionsHideTimerRef.current = null;
+    }, 950);
+  }, []);
+
+  useEffect(() => {
+    return () => {
+      if (scrollActionsHideTimerRef.current !== null) {
+        window.clearTimeout(scrollActionsHideTimerRef.current);
+      }
+    };
+  }, []);
+
   const scrollMessagesToLatest = useCallback((behavior: ScrollBehavior = "smooth") => {
     const scroll = () => {
       const surface = messagesSurfaceRef.current;
@@ -451,6 +475,7 @@ function WorkbenchPage({
 
       setComposerHidden(false);
       shouldFollowNewMessagesRef.current = true;
+      revealScrollActionsTemporarily("bottom");
       surface.scrollTo({ top: surface.scrollHeight, behavior });
       lastScrollTopRef.current = surface.scrollTop;
     };
@@ -459,7 +484,7 @@ function WorkbenchPage({
       scroll();
       window.setTimeout(scroll, 80);
     });
-  }, []);
+  }, [revealScrollActionsTemporarily]);
 
   const imageSettingGroups = useMemo<WorkbenchFieldGroup[]>(
     () => [
@@ -1373,6 +1398,9 @@ function WorkbenchPage({
       const delta = top - lastScrollTopRef.current;
       const atTop = top <= edgeThreshold;
       const atBottom = top + surface.clientHeight >= surface.scrollHeight - edgeThreshold;
+      if (surface.scrollHeight > surface.clientHeight + edgeThreshold && Math.abs(delta) > 1) {
+        revealScrollActionsTemporarily(delta > 0 ? "bottom" : "top");
+      }
       shouldFollowNewMessagesRef.current = atBottom;
       if (atTop || atBottom) {
         setComposerHidden(false);
@@ -1384,7 +1412,7 @@ function WorkbenchPage({
 
     surface.addEventListener("scroll", handleScroll, { passive: true });
     return () => surface.removeEventListener("scroll", handleScroll);
-  }, [hasActivatedWorkspace]);
+  }, [hasActivatedWorkspace, revealScrollActionsTemporarily]);
 
   const scrollMessagesSurface = useCallback((direction: "top" | "bottom") => {
     const surface = messagesSurfaceRef.current;
@@ -1392,8 +1420,9 @@ function WorkbenchPage({
 
     const top = direction === "top" ? 0 : surface.scrollHeight;
     setComposerHidden(false);
+    revealScrollActionsTemporarily(direction);
     surface.scrollTo({ top, behavior: "smooth" });
-  }, []);
+  }, [revealScrollActionsTemporarily]);
 
   const closeToolbarMenus = () => setToolbarMenuId(null);
   const toggleToolbarMenu = (menuId: Exclude<ToolbarMenuId, null>) => {
@@ -3022,10 +3051,13 @@ function WorkbenchPage({
                 {renderComposerToolbar(false, isGenerating)}
               </div>
             </section>
-            <div className="wb-chat-scroll-actions" aria-label="聊天滚动">
+            <div
+              className={`wb-chat-scroll-actions${scrollActionsVisible ? " is-visible" : ""}${scrollActionDirection ? ` is-${scrollActionDirection}` : ""}`}
+              aria-label="聊天滚动"
+            >
               <button
                 type="button"
-                className="wb-chat-scroll-actions__button"
+                className="wb-chat-scroll-actions__button wb-chat-scroll-actions__button--top"
                 title="返回聊天顶部"
                 aria-label="返回聊天顶部"
                 onClick={() => scrollMessagesSurface("top")}
@@ -3034,7 +3066,7 @@ function WorkbenchPage({
               </button>
               <button
                 type="button"
-                className="wb-chat-scroll-actions__button"
+                className="wb-chat-scroll-actions__button wb-chat-scroll-actions__button--bottom"
                 title="到达聊天底部"
                 aria-label="到达聊天底部"
                 onClick={() => scrollMessagesSurface("bottom")}