dev: NixOS 25.11 매뉴얼 로컬 사본 추가

nixpkgs nixos-25.11 브랜치의 nixos/doc/manual/ 디렉토리를 sparse clone으로
가져와 ~/obsidian/dev/nixos-manual/에 복사. _index.md에 구조/갱신 방법 정리.

오프라인 참조 + AI 에이전트 컨텍스트용. sandbox-tokyo 같은 NixOS 노드 운영 시
빠른 참조로 사용.

dev/nixos-manual/configuration/profiles/installation-device.section.md

@@ -0,0 +1,24 @@
+# Installation Device {#sec-profile-installation-device}
+
+Provides a basic configuration for installation devices like CDs.
+This enables redistributable firmware, includes the
+[Clone Config profile](#sec-profile-clone-config)
+and a copy of the Nixpkgs channel, so `nixos-install`
+works out of the box.
+
+Documentation for [Nixpkgs](#opt-documentation.enable)
+and [NixOS](#opt-documentation.nixos.enable) are
+forcefully enabled (to override the
+[Minimal profile](#sec-profile-minimal) preference); the
+NixOS manual is shown automatically on TTY 8, udisks is disabled.
+Autologin is enabled as `nixos` user, while passwordless
+login as both `root` and `nixos` is possible.
+Passwordless `sudo` is enabled too.
+[NetworkManager](#opt-networking.networkmanager.enable) is
+enabled and can be configured interactively with `nmtui`.
+
+It is explained how to login, start the ssh server, and if available,
+how to start the display manager.
+
+Several settings are tweaked so that the installer has a better chance of
+succeeding under low-memory environments.