fix: Remove ara data volume (MySQL backend), require ARA_SECRET_KEY 🐛

.env.example

@@ -15,8 +15,11 @@ ARA_DATABASE_PASSWORD=arasecret
 # ------------------------------------------------------------
 # ARA core
 # ------------------------------------------------------------
-# IMPORTANT: replace with a long random string in production
-ARA_SECRET_KEY=changeme_use_a_long_random_string
+# REQUIRED: generate with:
+#   python3 -c "import secrets; print(secrets.token_hex(50))"
+# Without this, a new random key is generated on every container
+# start — invalidating Django sessions and ARA's signed cookies.
+ARA_SECRET_KEY=
 
 # Timezone — controls BOTH crond scheduling AND ARA display times.
 # Use a tz database name: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones