feat: sync group call livestream support

deploy/migrations/0053_group_call_rtmp.up.sql

@@ -0,0 +1,10 @@
+-- Live Stream（RTMP 直播）：group_calls 增加 rtmp_stream 标记；
+-- per-channel 持久 RTMP 推流密钥（revoke 轮换后旧 key 立即失效）。
+ALTER TABLE group_calls
+    ADD COLUMN IF NOT EXISTS rtmp_stream boolean DEFAULT false NOT NULL;
+
+CREATE TABLE IF NOT EXISTS group_call_rtmp_keys (
+    channel_id bigint PRIMARY KEY,
+    stream_key text NOT NULL,
+    updated_at integer NOT NULL
+);