fix(workbench): stabilize investigation presentation rendering

Keep investigation graphs stable during updates, defer expensive chart rendering, and prevent stale results when switching tasks. Adopt reference annotations and consolidate frontend documentation.

src/features/workbench/components/presentation-history-switcher.tsx

@@ -99,8 +99,9 @@ export function PresentationHistorySwitcher({
       </div>
       {playback ? (
         <div className="flex min-w-0 items-center gap-2" role="group" aria-label="历史播放">
-          <Button type="button" variant="outline" size="icon-sm" className="size-8 shrink-0"
+          <Button type="button" variant="ghost" size="icon-sm" className="size-8 shrink-0 text-muted-foreground after:inset-0"
             aria-label={playback.playing ? "暂停历史播放" : "播放历史"}
+            title={playback.playing ? "暂停历史播放" : "播放历史"}
             disabled={!playable.length} onClick={playback.onToggle}>
             {playback.playing ? <Pause size={14} aria-hidden /> : <Play size={14} aria-hidden />}
           </Button>
@@ -113,8 +114,11 @@ export function PresentationHistorySwitcher({
             {selectedId === null ? playable.length : playable.length ? progress + 1 : 0}/{playable.length}
           </span>
           <Select value={String(playback.speed)} onValueChange={(value) => playback.onSpeedChange(Number(value))}>
-            <SelectTrigger aria-label="历史播放速度" className="h-8 w-[68px] shrink-0 gap-1 px-2 text-xs"><SelectValue /></SelectTrigger>
-            <SelectContent position="popper" className="workbench-shadcn-surface z-[90]">
+            <SelectTrigger aria-label="历史播放速度"
+              className="form-field-inset h-8 w-[54px] shrink-0 justify-center gap-1 border-0 px-1.5 text-xs tabular-nums text-muted-foreground shadow-none hover:bg-muted hover:text-foreground data-[state=open]:bg-muted data-[state=open]:text-foreground [&>svg]:size-3">
+              <SelectValue />
+            </SelectTrigger>
+            <SelectContent position="popper" align="end" sideOffset={4} className="workbench-shadcn-surface z-[90] min-w-[72px]">
               {[0.5, 1, 2].map((speed) => <SelectItem key={speed} value={String(speed)} className="text-xs">{speed}×</SelectItem>)}
             </SelectContent>
           </Select>