fix(playlist): drop stale per-item formats on re-probe

Peer-review of the exact-format-per-item feature: re-clicking "Preview
formats" on an already-loaded playlist reset info/playlist but left
itemFormats/itemFormatOptions/formatExpanded keyed by position, so a
stale exact-format pick could silently reattach to a different video
landing at the same index in the new probe result and flow into
addPlaylist(). Extracted resetPlaylistItemState() and call it from
both clearProbe() and fetchFormats().

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/renderer/src/components/downloadBar/useDownloadBar.ts

@@ -281,11 +281,11 @@ export function useDownloadBar(): DownloadBarController {
     playlist === null &&
     probeError === null
 
-  function clearProbe(): void {
+  // Per-entry format state is keyed by playlist position, so it must be dropped
-    setInfo(null)
+  // any time the playlist itself is dropped or re-fetched -- otherwise a stale
-    setProbeError(null)
+  // exact-format pick from a prior probe can silently reattach to a different
-    setFormatId('')
+  // video that lands at the same index in the new result.
-    setPlaylist(null)
+  function resetPlaylistItemState(): void {
     setSelected(new Set())
     setItemKinds({})
     setFormatExpanded(new Set())
@@ -295,6 +295,14 @@ export function useDownloadBar(): DownloadBarController {
     setFormatProbeError({})
   }
 
+  function clearProbe(): void {
+    setInfo(null)
+    setProbeError(null)
+    setFormatId('')
+    setPlaylist(null)
+    resetPlaylistItemState()
+  }
+
   // Reset the whole bar after a download / playlist is enqueued: clear the URL +
   // probe and drop the one-shot overrides (trim / schedule / advanced / incognito /
   // per-download options) so the next download starts from the global defaults.
@@ -387,6 +395,7 @@ export function useDownloadBar(): DownloadBarController {
     setProbeError(null)
     setInfo(null)
     setPlaylist(null)
+    resetPlaylistItemState()
     // Probing may switch the URL to the format-picker path, changing the command.
     setCommandPreview(null)
     try {