fix: 软刷新齐套前保留旧画面，避免一点击就卸光

Logo/下拉静默预热后一次覆盖；commit 不再先 reset/loading；顺带会话预取与可配置 Feed 排序标签。

frontend/src/components/TopProgressBar.tsx

@@ -0,0 +1,75 @@
+import { useEffect, useRef, useState } from 'react';
+import { subscribeSpaTransition } from '../utils/spaTransition';
+
+/**
+ * 视口顶部 2px 细进度条（类 Next.js / YouTube）。
+ * 由 spaTransition start/done 驱动，假进度爬升至约 80%，结束冲到 100%。
+ */
+export default function TopProgressBar() {
+  const [visible, setVisible] = useState(false);
+  const [width, setWidth] = useState(0);
+  const [fading, setFading] = useState(false);
+  const timerRef = useRef<ReturnType<typeof setInterval> | null>(null);
+  const fadeRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const activeRef = useRef(false);
+
+  useEffect(() => {
+    const clearTick = () => {
+      if (timerRef.current) {
+        clearInterval(timerRef.current);
+        timerRef.current = null;
+      }
+    };
+    const clearFade = () => {
+      if (fadeRef.current) {
+        clearTimeout(fadeRef.current);
+        fadeRef.current = null;
+      }
+    };
+
+    return subscribeSpaTransition((active) => {
+      if (active) {
+        activeRef.current = true;
+        clearFade();
+        setFading(false);
+        setVisible(true);
+        setWidth(12);
+        clearTick();
+        timerRef.current = setInterval(() => {
+          setWidth((w) => {
+            if (w >= 80) return w;
+            // 越接近 80 越慢
+            const step = Math.max(0.4, (80 - w) * 0.045);
+            return Math.min(80, w + step);
+          });
+        }, 120);
+        return;
+      }
+
+      if (!activeRef.current) return;
+      activeRef.current = false;
+      clearTick();
+      setWidth(100);
+      setFading(true);
+      clearFade();
+      fadeRef.current = setTimeout(() => {
+        setVisible(false);
+        setFading(false);
+        setWidth(0);
+      }, 220);
+    });
+  }, []);
+
+  if (!visible && width <= 0) return null;
+
+  return (
+    <div
+      className={[
+        'top-progress',
+        fading ? 'top-progress--done' : '',
+      ].filter(Boolean).join(' ')}
+      style={{ width: `${width}%` }}
+      aria-hidden
+    />
+  );
+}