Fix MLflow psycopg2 missing by installing psycopg2-binary at startup

The official MLflow image lacks psycopg2. Install it via pip before
starting the server. Also fix artifact root to use absolute path
inside the mounted volume.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -68,10 +68,13 @@ services:
       - "127.0.0.1:5000:5000"
     volumes:
       - mlflow-data:/mlflow
-    command: >
+    entrypoint: ["/bin/sh", "-c"]
+    command:
+      - |
+        pip install --quiet psycopg2-binary &&
         mlflow server
           --backend-store-uri "postgresql://${POSTGRES_USER}:${POSTGRES_PASSWORD}@postgres:5432/${POSTGRES_DB}"
-        --default-artifact-root ./mlruns/artifacts
+          --default-artifact-root /mlflow/artifacts
           --host 0.0.0.0
           --port 5000
     restart: unless-stopped