chore(call): pin element-call-embedded 0.25.0-lotus.21 (#43)

lotus.21 checks widget messages against the host's origin (works same- and
cross-origin) and accepts soundboard clip bytes. Same-origin behaviour is
unchanged; verified against the published package: join, both screenshare
paths, PTT/deafen in the frame, layout/reactions/settings, speaking and mic
level, soundboard, avatars, muted-speech warning, per-person volume, and the
foreign-frame spoof stays blocked.

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

package.json

@@ -108,7 +108,7 @@
   },
   "devDependencies": {
     "@axe-core/playwright": "4.13.0",
-    "@lotusguild/element-call-embedded": "0.25.0-lotus.20",
+    "@lotusguild/element-call-embedded": "0.25.0-lotus.21",
     "@playwright/test": "1.63.0",
     "@rollup/plugin-inject": "5.0.5",
     "@rollup/plugin-wasm": "6.2.2",