feat(call): optional Element Call origin via config.json elementCallUrl (#43)

Groundwork for serving the call page from its own origin
(call.chat.lotusguild.org). Inert until config.json sets `elementCallUrl`:
without it the bundled same-origin page is used exactly as today.

- callPageUrl: resolves `elementCallUrl` — absolute https only (http only on
  localhost for development); anything else, and the desktop app, fall back
  to the bundled page so a bad value can't break calls. Set once from the
  loaded client config.
- CallEmbed builds the widget URL from it; the widget origin (used by the
  message guard and Capability Delegation) follows automatically.
- Soundboard: a host blob: URL can't be fetched from another origin, so
  io.lotus.inject_audio now also carries the clip's bytes (`audio`). Forks
  that predate it ignore the field and use `url`, so this is safe on the
  released fork.

Needs element-call's lotus-call-origin branch (host-origin message check +
inject_audio bytes) released and pinned before `elementCallUrl` is set.

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

src/app/plugins/call/CallControl.ts

@@ -564,19 +564,27 @@ export class CallControl extends EventEmitter implements CallControlState {
    * track (`io.lotus.inject_audio`) rather than splicing the mic. `url` must be
    * an https/blob URL the widget can fetch WITHOUT credentials — the host
    * resolves an mxc clip to a `blob:` object URL first (authenticated media
-   * can't be fetched cross-realm by the widget). `volume` is 0–1.
+   * can't be fetched cross-realm by the widget) — and `audio` the same clip's
+   * bytes, which the fork prefers. `volume` is 0–1.
    *
    * The local user does not hear their own published track, so callers should
    * also play the clip locally for feedback.
    */
-  public injectAudio(url: string, volume = 1): Promise<{ played: boolean; reason?: string }> {
+  public injectAudio(
+    url: string,
+    volume = 1,
+    audio?: ArrayBuffer,
+  ): Promise<{ played: boolean; reason?: string }> {
     // [EC#13] The fork now refuses while the local mic is muted and replies
     // { played:false, reason:"muted" }; older forks reply {} (treated as played).
+    // [Gitea #43] `audio` carries the clip's bytes: a `blob:` URL only works on
+    // this origin, so a call page on its own origin can't fetch it. Forks that
+    // predate `audio` ignore it and use `url`.
     return this.call.transport
-      .send<{ url: string; volume: number }, { played?: boolean; reason?: string }>(
-        'io.lotus.inject_audio',
-        { url, volume },
-      )
+      .send<
+        { url: string; volume: number; audio?: ArrayBuffer },
+        { played?: boolean; reason?: string }
+      >('io.lotus.inject_audio', audio ? { url, volume, audio } : { url, volume })
       .then((r) => ({ played: r?.played !== false, reason: r?.reason }))
       .catch(() => ({ played: true }));
   }