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

docs/troubleshooting.md

@@ -8,7 +8,9 @@ Gitea's sanitized message, and the audit log has one event per call (see
 
 | Message or exit | Cause and fix |
 |---|---|
-| Exit code 2, "GITEA_TOKEN" required (stdio) | stdio needs `GITEA_TOKEN`. Put it in the client's `env` block or in `.env` in the working directory the client starts the server in. |
+| Exit code 2, "GITEA_TOKEN" required (stdio) | stdio needs `GITEA_TOKEN`. Put it in the client's `env` block, or in an env file passed with `--env-file` (or `AEGIS_ENV_FILE`). A `.env` in the working directory counts only when it is a regular file you own with mode 0600. |
+| Warning "ignoring ./.env: ..." | The working directory's `.env` is a symlink, owned by someone else or accessible to group or others, so its settings are not loaded. Run `chmod 600 .env`, or pass `--env-file PATH`. See "Which env file is read" in [configuration.md](configuration.md). |
+| Exit code 2, "env file ... does not exist" | The file named by `--env-file` or `AEGIS_ENV_FILE` is missing or not a regular file. |
 | Exit code 2, refuses a non-loopback bind | `MCP_HOST` is not loopback and there is no `MCP_BEARER_TOKEN` or complete OAuth setup. Set one of them, or bind `127.0.0.1` behind a reverse proxy. |
 | Exit code 2, lists OAuth settings | `OAUTH_ENABLED=true` needs `GITEA_OAUTH_CLIENT_ID`, `GITEA_OAUTH_CLIENT_SECRET`, `TOKEN_ENCRYPTION_KEY` and `PUBLIC_BASE_URL`. |
 | Validation error naming a setting | See the rules in [configuration.md](configuration.md): URLs must be http(s) without credentials, `PUBLIC_BASE_URL` must be https, secrets need 32 characters, `OAUTH_SCOPES` accepts only granular scopes. |