feat: 资料流标题+筛选吸顶,滚动时保持可见

把「全部资料」标题与筛选标签合并为一个吸顶块,钉在全局顶栏下方
(top-[64px]/md:top-[70px]),向下滚动时标题和筛选都不再消失,仅内容流滚动。
移除 FilterChips 原先吸到 top-0(藏到顶栏背后)的行为。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/messageStream/MessageStream.tsx

@@ -6,15 +6,17 @@ import type { PostScope } from "../../types/post";
 import { Reveal } from "../../motion";
 import { Skeleton } from "../Skeleton";
 import { FilterChips } from "./FilterChips";
+import { SectionHeader } from "../SectionHeader";
 import { MessageBubble } from "./MessageBubble";
 import { useGroupedByDay } from "./hooks/useGroupedByDay";
 import { usePostStream } from "./hooks/usePostStream";
 
 export type MessageStreamProps = {
   scope: PostScope;
+  title?: string;
 };
 
-export function MessageStream({ scope }: MessageStreamProps) {
+export function MessageStream({ scope, title }: MessageStreamProps) {
   const { t, lang } = useI18n();
   const [sp, setSp] = useSearchParams();
   const { hash } = useLocation();
@@ -114,7 +116,16 @@ export function MessageStream({ scope }: MessageStreamProps) {
 
   return (
     <div className="mx-auto max-w-full md:max-w-[820px] lg:max-w-[1080px] xl:max-w-[1180px]">
-      <FilterChips type={type} onTypeChange={(v) => updateParam("type", v)} />
+      {/* Title + filters stay pinned below the global header so users always
+          see which page they're on and can switch filters while scrolling. */}
+      <div className="sticky top-[64px] z-30 bg-ark-bg md:top-[70px]">
+        {title ? (
+          <div className="px-4 pb-1 pt-2 md:px-0">
+            <SectionHeader title={title} />
+          </div>
+        ) : null}
+        <FilterChips type={type} onTypeChange={(v) => updateParam("type", v)} />
+      </div>
 
       <div className="flex flex-col gap-3 px-4 pt-4 md:px-0 md:pt-2">
         {isInitialLoad ? (