feat(call): screenshare from inside the frame where delegation is missing; host stops reading the call frame (#43)

Firefox, Safari and the WebKitGTK desktop app can't hand the user's click to
the call frame (no Capability Delegation), and getDisplayMedia needs it. The
host used to click EC's hidden footer button through the DOM instead, which
dies with same-origin. Now (pins element-call-embedded 0.25.0-lotus.20):

- those engines get `lotusFrameScreenshare`, the fork shows EC's own
  screenshare button in the frame, and the call bar and status bar hide
  theirs once controls_state reports `frameScreenshare`; the
  screenshare-audio mute stays;
- the room's call policy is pushed with io.lotus.set_frame_screenshare, so
  the frame button hides where the server would refuse a share, like ours;
- Chromium keeps the delegated io.lotus.set_screenshare from the host bar.

Removed the fallbacks for forks older than lotus.14, which read or clicked
EC's DOM: the screenshare/layout/settings/reactions/leave button lookups
and their MutationObservers, the frame-window hotkey binding, and the
speaking/muted tile scrape in useCallSpeakers (io.lotus.call_state is the
only source now). getCallDocument is gone; the host's only handle on the
frame is postMessage.

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

src/app/plugins/call/CallEmbed.ts

@@ -28,7 +28,7 @@ import {
 import { CallControl } from './CallControl';
 import { CallControlState } from './CallControlState';
 import { verifyDenoiseAssets } from './denoiseSmokeCheck';
-import { getCallDocument } from './utils';
+import { canDelegateCapability } from './utils';
 
 // Maximum time to wait for the embedded Element Call iframe to progress from
 // initial load to a ready/joined state. If it hasn't by then, we assume the
@@ -218,6 +218,11 @@ export class CallEmbed {
       // [Gitea #43] The fork hides its own footer (we draw the call bar) and
       // sets its root color-scheme from the theme, instead of us injecting CSS.
       lotusHostControls: 'true',
+      // [Gitea #43] Engines without Capability Delegation (Firefox, Safari,
+      // WebKitGTK) can't start a share from our call bar: getDisplayMedia
+      // needs the click inside the frame. There the fork shows EC's own
+      // screenshare button and we hide ours.
+      ...(canDelegateCapability() ? {} : { lotusFrameScreenshare: 'true' }),
       // [lotus #3 / P5-15] Arm the fork's audio-inject handler so the in-call
       // soundboard can publish clips into the call. Dormant until the host
       // sends io.lotus.inject_audio (only on an explicit user click), so
@@ -311,10 +316,6 @@ export class CallEmbed {
     const controlState = initialControlState ?? new CallControlState(true, false, true);
     this.control = new CallControl(controlState, call, iframe);
     this.initialState = controlState;
-    this.control.startObserving();
-    iframe.onload = () => {
-      this.control.startObserving();
-    };
     // If the iframe document itself fails to load, fail fast.
     iframe.onerror = () => {
       this.settleLoad('iframe');
@@ -348,10 +349,6 @@ export class CallEmbed {
     return this.room.roomId;
   }
 
-  get document(): Document | undefined {
-    return getCallDocument(this.iframe);
-  }
-
   public setTheme(theme: ElementCallThemeKind) {
     this.themeKind = theme;
     return this.call.transport
@@ -573,13 +570,12 @@ export class CallEmbed {
 
   private onCallJoined(): void {
     this.settleLoad();
-    this.control.startObserving();
 
     // C-H1: EC fires JoinCall again on an EC reconnect (this action has no
     // once-guard). forceState() would reset live mic/video/deafen back to the
     // join-time snapshot, so only run it on the FIRST join. On a rejoin we just
-    // re-apply styles/observers (above) and re-push the sticky fork state
-    // (deafen/quality), leaving the user's live media state untouched.
+    // re-push the sticky fork state (deafen/quality), leaving the user's live
+    // media state untouched.
     if (this.joined) {
       this.control.resendForkState();
       return;