claude-code: Add support for installing plugins (#8934)

Allow for configuring marketplaces or individual plugins.

Both are provided as a list of either paths or packages.

The lone plugins are enabled by adding a --plugin-dir argument to the wrapper script.

Marketplaces are saved to the nix store and enabled by adding to the claude settings and known_marketplaces files.

With the marketplace "installed", the plugin can just be enabled via the enabledPlugins setting.

tests/modules/programs/claude-code/plugins.nix

@@ -0,0 +1,28 @@
+{ config, ... }:
+
+{
+  programs.claude-code = {
+    package = config.lib.test.mkStubPackage {
+      name = "claude-code";
+      buildScript = ''
+        mkdir -p $out/bin
+        touch $out/bin/claude
+        chmod 755 $out/bin/claude
+      '';
+    };
+    enable = true;
+
+    plugins = [ ./test-plugin ];
+  };
+
+  nmt.script = ''
+    wrapperPath="$TESTED/home-path/bin/claude"
+    normalizedWrapper=$(normalizeStorePaths "$wrapperPath")
+    assertFileContent $normalizedWrapper ${./expected-plugin-wrapper}
+
+    test "$(grep -o -- '--plugin-dir ' "$wrapperPath" | wc -l)" -eq 1
+    pluginDir=$(grep -o -- '--plugin-dir /nix/store/[^ ]*' "$wrapperPath")
+    pluginDir="''${pluginDir#--plugin-dir }"
+    assertFileContent "$pluginDir/.claude-plugin/plugin.json" ${./test-plugin/.claude-plugin/plugin.json}
+  '';
+}