docs(install): cover Docker and native deployments

docs/ENVIRONMENT.md

@@ -1,6 +1,6 @@
 # Environment variable reference
 
-The public [Portainer stack](../compose.yml) needs **no environment variables**.
+The public [Docker Compose/Portainer stack](../compose.yml) needs **no environment variables**.
 Its image supplies the runtime defaults; use the first-run setup wizard to set
 the application URL, connect services and configure notifications. The normal
 stack does not need a Dockerfile, source checkout or `.env` file.
@@ -8,6 +8,8 @@ stack does not need a Dockerfile, source checkout or `.env` file.
 This reference also covers advanced/manual deployments, compatibility aliases,
 image-build inputs and repository-only tooling. A variable being listed here
 does **not** mean that it belongs in the public Compose file.
+For non-container deployments, follow the explicit configuration steps in
+[native Linux installation](NATIVE_INSTALL.md) or [foreground installation](LOCAL_DEVELOPMENT.md).
 
 ## Managed installation defaults and precedence
 
@@ -31,8 +33,9 @@ does **not** mean that it belongs in the public Compose file.
   deployment controls, not ordinary editable settings. Container listener ports
   are fixed by its process supervisor, not by application settings.
 - For manual deployments, environment variables are read at process startup.
-  Restart/recreate after changing them. A `.env` file is loaded by the relevant
-  Compose template's `env_file`, not automatically discovered by the application.
+  Restart/recreate after changing them. Load the private file through the relevant
+  manual Compose template's `env_file`, native systemd `EnvironmentFile`, or
+  foreground Uvicorn `--env-file`; it is not automatically discovered by the application.
   Keep manual credentials stable across upgrades and offline restores.
 
 Defaults use JSON notation: `null` means unset, `""` means an empty string,