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/configuration.md

@@ -0,0 +1,28 @@
+# Configuration {#ch-configuration}
+
+This chapter describes how to configure various aspects of a NixOS machine through the configuration file {file}`/etc/nixos/configuration.nix`. As described in [](#sec-changing-config), changes to this file only take effect after you run {command}`nixos-rebuild`.
+
+```{=include=} chapters
+config-syntax.chapter.md
+package-mgmt.chapter.md
+user-mgmt.chapter.md
+file-systems.chapter.md
+x-windows.chapter.md
+wayland.chapter.md
+gpu-accel.chapter.md
+xfce.chapter.md
+networking.chapter.md
+linux-kernel.chapter.md
+subversion.chapter.md
+```
+
+```{=include=} chapters
+@MODULE_CHAPTERS@
+```
+
+```{=include=} chapters
+profiles.chapter.md
+mattermost.chapter.md
+kubernetes.chapter.md
+```
+<!-- Apache; libvirtd virtualisation -->