fix: load ./.env only when private and owned, add --env-file and AEGIS_ENV_FILE (SEC-04)

docs/getting-started.md

@@ -29,7 +29,7 @@ Setup prompts for the Gitea URL and the token (hidden input). For unattended use
 | `--gitea-url` | Gitea base URL |
 | `--public-base-url` | Public https URL of this server. Enables registration of the OAuth application |
 | `--no-oauth` | Do not create the Gitea OAuth application |
-| `--env-file` | Env file to create or update (default `./.env`) |
+| `--env-file` | Env file to create or update (default `AEGIS_ENV_FILE`, else `./.env`) |
 | `--template` | Env template (default `./.env.example`, else the copy built into the package) |
 | `--yes` | Never prompt, and accept regenerating an OAuth client secret |