fix: "Show in folder" reveals in the explorer instead of opening a directory in the editor

The open-path interception reroutes EVERY chat-side file open into the
sidebar editor, including the stock "Show in folder" gesture: the
ui-deliverables row passes "." (resolved to "<cwd>/." by the chat view),
so clicking it opened a bogus editor tab for the workspace directory
(host error: '"..." is a directory').

- openpath-intercept: detect the folder-reveal gesture ("." / "./" /
  "<cwd>/.") and route it to a new revealInExplorer dep instead of the editor.
- intercept: revealInExplorer switches to the explorer tab (expanding the
  panel), expands the produced files' parent directories, and highlights /
  scrolls to them; the intercepted produced-files row now also renders its
  own "Show in folder" button when files are hidden.
- produced-files: selectProducedFiles reads the engine Turn data
  (owner.turn.data.get("deliverables")) — the same source ui-deliverables
  uses — with the node replica as fallback. The old code read owner.nodes,
  which the real TurnTailOwnerProps ({turn, seq, openFile}) does not carry,
  so the takeover never claimed the chain.
- state: transient `revealed` set (never persisted) plus a revealPaths
  reducer that expands ancestor directories.
- ExplorerView: highlight + scroll revealed rows; Sidebar/tabs/service
  thread `revealed` through TabComponentProps.
- tests: folder-gesture routing, engine-data selector, wiring seat, zh/en copy.

src/client/builtins/tabs.tsx

@@ -79,11 +79,12 @@ export function builtinTabs(ctx: Context): readonly TabDescriptor[] {
       icon: (size: number) => <IconFolderOpen16 size={size} />,
       order: 10,
       single: true,
-      component: ({ ctx, store, scope, expanded, onToggleDir, onReferenceFile }) => (
+      component: ({ ctx, store, scope, expanded, revealed, onToggleDir, onReferenceFile }) => (
         <ExplorerView
           sessionId={scope.sessionId}
           cwd={scope.cwd}
           expanded={expanded ?? []}
+          revealed={revealed ?? []}
           onToggle={onToggleDir ?? (() => { /* no-op */ })}
           onOpenFile={(path) => { openSidebarFile(ctx, store, scope.sessionId, path) }}
           onReferenceFile={onReferenceFile ?? (() => { /* no-op */ })}