lib/nix: use locked nixpkgs for maintainer extraction

Importing <nixpkgs> tied extraction to the caller's NIX_PATH. When that
channel lacks a maintainer referenced through `with lib.maintainers`
(such as sherlock's `_74k1`, which exists in the locked nixpkgs but not
in an older channel), evaluation fails outright and the generated list
varies by machine. Resolve nixpkgs from flake.lock so extraction matches
what Home Manager builds with.

Also classify maintainers by identity (github/name) rather than attribute
name so renamed entries like `_9p4` still match, and correct the
arguments passed to the manual derivation so its maintainer is collected.

lib/nix/extract-maintainers-meta.nix

@@ -1,7 +1,14 @@
 # Extract maintainers from Home Manager modules using meta.maintainers
 # This script evaluates all Home Manager modules and extracts the merged maintainer information
 let
-  pkgs = import <nixpkgs> { };
+  flakeLock = builtins.fromJSON (builtins.readFile ../../flake.lock);
+  nixpkgsNodeName = flakeLock.nodes.root.inputs.nixpkgs;
+  nixpkgsLocked = flakeLock.nodes.${nixpkgsNodeName}.locked;
+
+  pkgs = import (fetchTarball {
+    url = "https://github.com/${nixpkgsLocked.owner}/${nixpkgsLocked.repo}/archive/${nixpkgsLocked.rev}.tar.gz";
+    sha256 = nixpkgsLocked.narHash;
+  }) { };
   lib = import ../../modules/lib/stdlib-extended.nix pkgs.lib;
   releaseInfo = pkgs.lib.importJSON ../../release.json;
 
@@ -25,18 +32,23 @@ let
         file:
         let
           fileContent = import file;
+          # Arguments expected by docs/home-manager-manual.nix.
           evaluated =
             if lib.isFunction fileContent then
               fileContent {
-                inherit (pkgs) stdenv lib;
+                inherit lib;
-                documentation-highlighter = { };
+                inherit (pkgs)
+                  callPackage
+                  mdbook
+                  python3
+                  stdenv
+                  ;
                 revision = "unknown";
                 home-manager-options = {
                   home-manager = { };
                   nixos = { };
                   nix-darwin = { };
                 };
-                nixos-render-docs = { };
               }
             else
               fileContent;
@@ -59,27 +71,30 @@ let
 
   allMaintainerObjects = extractMaintainerObjects maintainers ++ additionalMaintainerObjects;
 
-  allMaintainerNames = lib.filter (name: name != null) (
+  getMaintainerName = maintainer: maintainer.github or maintainer.name or null;
-    map (maintainer: maintainer.github or maintainer.name or null) allMaintainerObjects
+
-  );
+  allMaintainerNames = lib.filter (name: name != null) (map getMaintainerName allMaintainerObjects);
 
   hmMaintainers = import ../../modules/lib/maintainers.nix;
-  hmMaintainerNames = lib.attrNames hmMaintainers;
+  hmMaintainerNames = lib.filter (name: name != null) (
+    map getMaintainerName (lib.attrValues hmMaintainers)
+  );
 
   maintainerDetails = lib.pipe allMaintainerObjects [
     (lib.filter (obj: (obj.github or obj.name or null) != null))
-    (map (obj: {
+    (map (
-      name = obj.github or obj.name;
+      obj:
-      value = obj // {
+      let
-        source =
+        maintainerName = obj.github or obj.name;
-          if categorizedMaintainers.home-manager ? ${obj.github} then
+      in
-            "home-manager"
+      {
-          else if categorizedMaintainers.nixpkgs ? ${obj.github} then
+        name = maintainerName;
-            "nixpkgs"
+        value = obj // {
-          else
+          source =
-            throw "${obj.github} is neither a home-manager or nixpkgs maintainer";
+            if categorizedMaintainers.home-manager ? ${maintainerName} then "home-manager" else "nixpkgs";
-      };
+        };
-    }))
+      }
+    ))
     lib.listToAttrs
   ];