feat(lotus): io.lotus.set_screenshare for the host call bar (cinny #43)

toWidget `io.lotus.set_screenshare { on?: boolean }` (omit to toggle)
starts/stops sharing via the view model instead of the host clicking EC's
hidden button. The host sends it with Capability Delegation
(`delegate: "display-capture"`) where supported, so getDisplayMedia keeps
the user's click on engines that require it. `controls_state` now carries
`screenshareAction: true` so the host only uses it on a fork that has it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/lotus/lotusActions.ts

@@ -75,7 +75,15 @@ export enum LotusWidgetActions {
   /** toWidget: toggle the reactions / raise-hand menu (cinny #43). */
   ToggleReactions = "io.lotus.toggle_reactions",
   /**
-   * fromWidget: `{ screensharing: boolean, layout: "grid" | "spotlight" | null }`
+   * toWidget: start/stop sharing `{ on?: boolean }` (omit to toggle; cinny #43).
+   * Starting calls getDisplayMedia, which needs the user's click: the host
+   * sends this with Capability Delegation (`delegate: "display-capture"`), and
+   * without it the browser rejects the share.
+   */
+  SetScreenshare = "io.lotus.set_screenshare",
+  /**
+   * fromWidget: `{ screensharing: boolean, layout: "grid" | "spotlight" | null,
+   * screenshareAction: true }`
    * whenever either changes (cinny #43), so the host stops reading EC's DOM for
    * them. Its arrival also tells the host this fork supports the actions above.
    */
@@ -98,4 +106,5 @@ export const LOTUS_TO_WIDGET_ACTIONS: LotusWidgetActions[] = [
   LotusWidgetActions.SetLayout,
   LotusWidgetActions.OpenSettings,
   LotusWidgetActions.ToggleReactions,
+  LotusWidgetActions.SetScreenshare,
 ];