lotus(#4): focus-participant spotlight via widget action

Adds io.lotus.focus_participant (toWidget): the host can pin a participant
to the spotlight by Matrix user id (or clear with userId:null), via a
manual override injected into CallViewModel.spotlightSpeaker$. Replaces
cinny's fragile DOM .click() tile-selector focus hack. Extracts the action
enum into lotusActions.ts (no circular import) and allow-lists Lotus
toWidget actions in initializeWidget. Additive: no-op unless the host
sends the action.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lotus/lotusFocus.ts

@@ -0,0 +1,38 @@
+/*
+Copyright 2026 Lotus Guild
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type IWidgetApiRequest } from "matrix-widget-api";
+
+import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
+import { widget } from "../widget";
+import { LotusWidgetActions } from "./lotusActions";
+
+/**
+ * Handle the host's `io.lotus.focus_participant` toWidget action (#4): pin a
+ * participant to the spotlight by Matrix user id, or clear it with
+ * `{ userId: null }`. This replaces cinny's old DOM `.click()` tile-selector
+ * hack with a real, layout-aware spotlight override.
+ *
+ * No effect unless the host actually sends the action, so registering the
+ * handler whenever we're a widget is safe. Returns a teardown function.
+ */
+export function startLotusFocus(vm: CallViewModel): () => void {
+  const w = widget;
+  if (!w) return () => undefined;
+
+  const handler = (ev: CustomEvent<IWidgetApiRequest>): void => {
+    // Always reply so the host transport doesn't time out.
+    void w.api.transport.reply(ev.detail, {});
+    const data = ev.detail.data as { userId?: unknown } | undefined;
+    const userId = typeof data?.userId === "string" ? data.userId : null;
+    vm.setManualSpotlight(userId);
+  };
+
+  w.lazyActions.on(LotusWidgetActions.FocusParticipant, handler);
+  return () =>
+    w.lazyActions.off(LotusWidgetActions.FocusParticipant, handler);
+}