Lotus fork: rename embedded package + add Gitea CI

- embedded/web/package.json: publish as @lotusguild/element-call-embedded
  from our Gitea fork (repository URL updated).
- .gitea/workflows/ci.yml: build the embedded bundle on PR/push to lotus;
  publish to the Gitea npm registry on a v* tag. Linux-only (web bundle).

Based on upstream element-call v0.20.1 (2d74c48).

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

embedded/web/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "@element-hq/element-call-embedded",
+  "name": "@lotusguild/element-call-embedded",
   "version": "0.0.0",
   "files": [
     "README.md",
@@ -9,6 +9,6 @@
   ],
   "repository": {
     "type": "git",
-    "url": "git+https://github.com/element-hq/element-call.git"
+    "url": "git+https://code.lotusguild.org/LotusGuild/element-call.git"
   }
 }