feat: add broadcast session tracking and chatlog service with database migrations

broadcasters/migrations/2_create_chatlog.up.sql

@@ -0,0 +1,9 @@
+CREATE TABLE chatlog (
+    id BIGSERIAL PRIMARY KEY,
+    timestamp TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    room UUID NOT NULL,
+    type TEXT NOT NULL CHECK (type IN ('ACTION','MESSAGE','ALLERT','CMD')),
+    data TEXT NOT NULL
+);
+
+CREATE INDEX idx_chatlog_room ON chatlog(room);