feat(media): add phase5 media provider abstraction and stream credentials APIs

Backend/drizzle/0008_media_plane_columns.sql

@@ -0,0 +1,4 @@
+ALTER TABLE "stream_sessions" ADD COLUMN "media_provider" varchar(32) DEFAULT 'mock' NOT NULL;--> statement-breakpoint
+ALTER TABLE "stream_sessions" ADD COLUMN "media_session_id" varchar(255);--> statement-breakpoint
+ALTER TABLE "stream_sessions" ADD COLUMN "publish_endpoint" text;--> statement-breakpoint
+ALTER TABLE "stream_sessions" ADD COLUMN "subscribe_endpoint" text;

Backend/drizzle/meta/_journal.json

@@ -57,6 +57,13 @@
       "when": 1770414956419,
       "tag": "0007_live_stream_sessions",
       "breakpoints": true
+    },
+    {
+      "idx": 8,
+      "version": "7",
+      "when": 1770415956419,
+      "tag": "0008_media_plane_columns",
+      "breakpoints": true
     }
   ]
 }