feat(web): 前端插槽设施，作品页与整理记录行挂「补字幕」

- lib/slots.ts 按位置注册(侧栏入口、作品页操作区 / 面板区、整理记录行操作、设置分区),默认直接显示;
  components/slots 挂载点:面板类直接渲染,动作类渲染成按钮 / 菜单项、对话框在菜单外渲染
- 作品页操作区与面板区、整理记录行菜单接入插槽;补字幕改由 features/subtitles.tsx 注册,
  作品页按钮行为不变,整理记录行菜单新增「补字幕」(成功 / 部分成功的入库类整理)

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Cxwgnn2pbzQ7rXv3rq7fei

apps/web/app/components/slots/slot-mounts.tsx

@@ -0,0 +1,57 @@
+import { type ComponentType, type ReactNode, useState } from "react";
+import "~/features/index.ts";
+import {
+  type ActionPosition,
+  type ActionSlot,
+  type PanelPosition,
+  type PanelSlot,
+  type SlotProps,
+  type SlotRegistry,
+  slots,
+  visibleActions,
+} from "~/lib/slots.ts";
+
+// 插槽挂载点(ADR-006)。功能在 app/features/*.tsx 里注册,这里只负责在页面上渲染;没有注册时什么都不渲染。
+
+/** 面板类插槽:按顺序渲染所有注册的组件 */
+export function SlotPanels<P extends PanelPosition>({
+  position,
+  props,
+  registry = slots,
+}: {
+  position: P;
+  props: SlotProps[P];
+  registry?: SlotRegistry;
+}) {
+  const entries = registry.entries(position) as PanelSlot<P>[];
+  if (entries.length === 0) return null;
+  return (
+    <>
+      {entries.map(({ id, Component }) => (
+        <Component key={id} {...props} />
+      ))}
+    </>
+  );
+}
+
+/**
+ * 动作类插槽:返回可见的项(页面按自己的样式渲染成按钮或菜单项)和当前打开的对话框。
+ * 对话框由页面渲染在菜单外面(菜单关了对话框也不会跟着卸载)。
+ */
+export function useSlotActions<P extends ActionPosition>(
+  position: P,
+  registry: SlotRegistry = slots,
+): {
+  items: (props: SlotProps[P]) => ActionSlot<P>[];
+  open: (entry: ActionSlot<P>, props: SlotProps[P]) => void;
+  dialog: ReactNode;
+} {
+  const [active, setActive] = useState<{ entry: ActionSlot<P>; props: SlotProps[P] } | null>(null);
+  // 泛型位置的 props 与 IntrinsicAttributes 交不出来,这里按具体对象渲染
+  const Dialog = active?.entry.Dialog as ComponentType<{ onClose: () => void }> | undefined;
+  return {
+    items: (props) => visibleActions(registry, position, props),
+    open: (entry, props) => setActive({ entry, props }),
+    dialog: Dialog && active ? <Dialog {...(active.props as object)} onClose={() => setActive(null)} /> : null,
+  };
+}