refactor(vibe): simplify durable session flow

docker-compose.yml

@@ -32,10 +32,6 @@ services:
       TYPESENSE_API_KEY: ${TYPESENSE_API_KEY}
       MUZICK_API_KEY: ${MUZICK_API_KEY}
       MUZICK_ADMIN_KEY: ${MUZICK_ADMIN_KEY}
-      # Durable Vibe sessions are intentionally bound to this configured,
-      # server-trusted owner instead of accepting a client-supplied user id.
-      # Set it to the UUID of the local Muzick user in .env.
-      MUZICK_VIBE_USER_ID: ${MUZICK_VIBE_USER_ID}
       MUSIC_DIR: /music
     volumes:
       # READ-ONLY, deliberately. Nothing in the API request path may write to