feat: enforce deployment environment preflight

docs/DEPLOYMENT.md

@@ -35,8 +35,9 @@ provider's HTTPS endpoint and provide its token through
 `PRICING_HTTP_PROVIDER_TOKEN` when required. Production startup rejects the
 fixture provider, missing endpoints, and non-HTTPS endpoints.
 
-Load the deployment environment into the shell and run the side-effect-free
-preflight before deploying:
+The deploy and rollback scripts load `PRODUCTION_ENV_FILE` (default `.env`)
+and run the side-effect-free preflight before touching Compose. Run them from
+the repository root:
 
 ```sh
 set -a
@@ -45,6 +46,9 @@ set +a
 ./scripts/validate-production-env.sh
 ```
 
+To use a separate production file, set `PRODUCTION_ENV_FILE=/secure/path/.env`
+when invoking the deploy or rollback script.
+
 Start the stack and apply migrations with:
 
 ```sh