multistreaming: scenes/composition, installer build support, service updates

- multistreaming (new): RTMP ingest + multi-platform fan-out with pluggable providers (Twitch/YouTube/Kick/custom), zero-knowledge key vaults, Authelia OIDC auth, shared rooms with editor/streamer roles, single-use invites, per-account streaming grants, and scenes & composition (grid/PiP layouts, text/image overlays, per-output audio routing).
- installer: support Dockerfile build in metadata (not just image) and RSA key generation for the Authelia OIDC JWKS.
- authelia: add OIDC provider with portainer + multistreaming clients (public + PKCE).
- services: remove allprox; add nginx-proxy-manager and portainer; update lldap; regenerate catalog.

services/multistreaming/src/id.js

@@ -0,0 +1,22 @@
+'use strict';
+
+const crypto = require('crypto');
+
+/** Random UUID v4. */
+function uuid() {
+  return crypto.randomUUID();
+}
+
+/** Random opaque token (invites, stream keys). */
+function token(bytes = 24) {
+  return crypto.randomBytes(bytes).toString('hex');
+}
+
+/** Constant-time string comparison. */
+function safeEqual(a, b) {
+  const ba = Buffer.from(String(a));
+  const bb = Buffer.from(String(b));
+  return ba.length === bb.length && crypto.timingSafeEqual(ba, bb);
+}
+
+module.exports = { uuid, token, safeEqual };