build(compose): use canonical compose files

compose.dev.yaml

@@ -0,0 +1,11 @@
+# Development runtime: bot only, connecting to the shared Atlas cluster.
+# There is no local datastore; set MONGODB_URI in .env. This file targets the
+# development database (the MONGODB_DATABASE below overrides any .env value).
+services:
+  bot:
+    build: .
+    env_file:
+      - .env
+    environment:
+      MONGODB_DATABASE: development
+    restart: unless-stopped