Fix wave chunk 1: cross-surface settings signal, dialog scroll-lock, noneRow retired

- lh:settings-saved CustomEvent (the lh:chat-renamed pattern, owner
  ruling): every writer (composer save, SetupDialog save, the settings
  write seam — one dispatch point carrying the section) notifies after a
  successful PUT; every reader re-reads its own seam: ModelControl's
  record read, the Agent section's slots/catalog, and chat.tsx's
  configured state (clearing slots mid-session now surfaces the setup
  CTA without a reload). Self-notifications re-read idempotently.
- MenuShell now announces lh:menu-open/lh:menu-close (still placement-
  only); the settings dialog's content column locks (overflow-hidden,
  count-based) while any menu is open — wheel-scrolling with a dropdown
  down is dead; the re-place-on-scroll fallback stays for un-lockable
  surfaces.
- The settings thinking menus' 'Default' noneRow is retired (owner:
  the unset state can't re-enter once chunk 2's auto-populate lands; no
  unpin is needed).
- Live-caught regression from the MenuShell migration fixed: the
  composer's outside-click handler never learned the portaled menu body
  isn't a container descendant — menu-row pointerdowns counted as
  outside and ATE THE PICK (composer picks have been dead for pointer
  users since 221c99d); rows now carve out via [data-lh-menu], the
  settings sections' discipline.
- Item 4 (resolved-level display for legacy records) deferred to chunk 2
  per owner ruling — the payload omits the level for legacy no-level
  records and DEFAULT_THINKING_ORDER was server-only (now in the core
  barrel via bd68486, exactly the seam chunk 2 needs).

components/settings-signal.ts

@@ -0,0 +1,47 @@
+"use client";
+
+/**
+ * THE cross-surface settings signal (fix wave, owner ruling 2026-09-22):
+ * every WRITER dispatches after a successful PUT, every READER re-reads —
+ * the composer reflects the strong slot the instant setup saves, the
+ * settings section reflects the composer's pick on its next mount... and
+ * so on, by construction. CustomEvent on the window, the lh:chat-renamed
+ * pattern: writers and readers live in different component subtrees
+ * (portaled dialogs included), and the app already speaks this dialect.
+ *
+ * The event carries the section name so ONE event serves all sections —
+ * readers filter on what they actually read.
+ */
+import { useEffect, useRef } from "react";
+
+export const SETTINGS_SAVED_EVENT = "lh:settings-saved";
+
+/** The settings sections a writer can land (the write seam's union). */
+export type SettingsSection = "general" | "agent" | "models" | "appearance" | "graph";
+
+/** Writers call this after the PUT resolves ok — never before (a failed
+ *  write notifies nothing; the record is unchanged). */
+export function notifySettingsSaved(section: SettingsSection): void {
+	window.dispatchEvent(
+		new CustomEvent(SETTINGS_SAVED_EVENT, { detail: { section } }),
+	);
+}
+
+/** Non-hook listener (imperative seams, tests). Returns an unsubscribe. */
+export function onSettingsSaved(handler: (section: SettingsSection) => void): () => void {
+	const listener = (e: Event) => {
+		const section = (e as CustomEvent<{ section?: SettingsSection }>).detail?.section;
+		if (section !== undefined) handler(section);
+	};
+	window.addEventListener(SETTINGS_SAVED_EVENT, listener);
+	return () => window.removeEventListener(SETTINGS_SAVED_EVENT, listener);
+}
+
+/** Reader subscription: re-invokes whenever a writer lands, with the
+ *  handler captured through a ref so callers never churn the
+ *  subscription (and never stale-close over it either). */
+export function useSettingsSaved(handler: (section: SettingsSection) => void): void {
+	const saved = useRef(handler);
+	saved.current = handler;
+	useEffect(() => onSettingsSaved((section) => saved.current(section)), []);
+}