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.chapter.md

@@ -0,0 +1,33 @@
+# Profiles {#ch-profiles}
+
+In some cases, it may be desirable to take advantage of commonly-used,
+predefined configurations provided by nixpkgs, but different from those
+that come as default. This is a role fulfilled by NixOS's Profiles,
+which come as files living in `<nixpkgs/nixos/modules/profiles>`. That
+is to say, expected usage is to add them to the imports list of your
+`/etc/configuration.nix` as such:
+
+```nix
+{ imports = [ <nixpkgs/nixos/modules/profiles/profile-name.nix> ]; }
+```
+
+Even if some of these profiles seem only useful in the context of
+install media, many are actually intended to be used in real installs.
+
+What follows is a brief explanation of the purpose and use-case for each
+profile. Detailing each option configured by each one is out of scope.
+
+```{=include=} sections
+profiles/all-hardware.section.md
+profiles/base.section.md
+profiles/clone-config.section.md
+profiles/demo.section.md
+profiles/docker-container.section.md
+profiles/graphical.section.md
+profiles/hardened.section.md
+profiles/headless.section.md
+profiles/installation-device.section.md
+profiles/perlless.section.md
+profiles/minimal.section.md
+profiles/qemu-guest.section.md
+```