feat: add freebuff package (Codebuff AI coding agent)

Add freebuff v0.0.85 from npm registry — a pure JS CLI tool for
AI-assisted coding. Pre-fetches all transitive npm dependencies to
work within the Nix sandbox (no network access during build).

packages/freebuff/default.nix

@@ -0,0 +1 @@
+{ pkgs, ... }: pkgs.callPackage ./package.nix { }

packages/freebuff/package.nix

@@ -0,0 +1,104 @@
+{
+  lib,
+  stdenv,
+  fetchurl,
+  nodejs,
+  makeWrapper,
+}:
+
+let
+  version = "0.0.85";
+
+  freebuffSrc = fetchurl {
+    url = "https://registry.npmjs.org/freebuff/-/freebuff-${version}.tgz";
+    hash = "sha256-1x593yLMkoFIO5O+k5NKeEpi729VhINQlW1xFbYGnXM=";
+  };
+
+  pkgTar = fetchurl {
+    url = "https://registry.npmjs.org/tar/-/tar-7.5.15.tgz";
+    hash = "sha256-hl60jJtM1W2THQyGZj8G72GEG8QvVrHvNnr7EU1liBw=";
+  };
+
+  pkgFsMinipass = fetchurl {
+    url = "https://registry.npmjs.org/@isaacs/fs-minipass/-/fs-minipass-4.0.1.tgz";
+    hash = "sha256-esKG48zMHqiYDnniA53va7l9MYLheVHNkJTwQA7ZgjY=";
+  };
+
+  pkgChownr = fetchurl {
+    url = "https://registry.npmjs.org/chownr/-/chownr-3.0.0.tgz";
+    hash = "sha256-TCT12qYwFCJS2oneZV998JDqR5RQqIJYl3UdeDIbE2A=";
+  };
+
+  pkgMinipass = fetchurl {
+    url = "https://registry.npmjs.org/minipass/-/minipass-7.1.3.tgz";
+    hash = "sha256-UqxhvnQ3VeP9yY5WAIbQ1KHix/02Qzh3kts44yLSfRI=";
+  };
+
+  pkgMinizlib = fetchurl {
+    url = "https://registry.npmjs.org/minizlib/-/minizlib-3.1.0.tgz";
+    hash = "sha256-mb8uKWGBct1x8GVHN0kMaPcbx+I3nUc+OPn+8tvs4uM=";
+  };
+
+  pkgYallist = fetchurl {
+    url = "https://registry.npmjs.org/yallist/-/yallist-5.0.0.tgz";
+    hash = "sha256-fJ1D26t8qzsxM7Dmpa8UAUSCKFMWs57J9QjvrdnrzpU=";
+  };
+
+in
+
+stdenv.mkDerivation rec {
+  pname = "freebuff";
+  version = "0.0.85";
+
+  src = freebuffSrc;
+
+  nativeBuildInputs = [ makeWrapper ];
+
+  installPhase = ''
+    runHook preInstall
+
+    mkdir -p "$out/lib/node_modules/freebuff"
+    cp -r * "$out/lib/node_modules/freebuff/"
+
+    # Extract npm dependencies from pre-fetched tarballs
+    extractNpmPkg() {
+      local src="$1" target="$2"
+      mkdir -p "$target"
+      tar xzf "$src" -C "$target" --strip-components=1
+    }
+
+    extractNpmPkg "${pkgTar}" "$out/lib/node_modules/tar"
+    extractNpmPkg "${pkgChownr}" "$out/lib/node_modules/chownr"
+    extractNpmPkg "${pkgMinipass}" "$out/lib/node_modules/minipass"
+    extractNpmPkg "${pkgMinizlib}" "$out/lib/node_modules/minizlib"
+    extractNpmPkg "${pkgYallist}" "$out/lib/node_modules/yallist"
+    mkdir -p "$out/lib/node_modules/@isaacs"
+    extractNpmPkg "${pkgFsMinipass}" "$out/lib/node_modules/@isaacs/fs-minipass"
+
+    mkdir -p "$out/bin"
+    makeWrapper "${nodejs}/bin/node" "$out/bin/freebuff" \
+      --set NODE_PATH "$out/lib/node_modules" \
+      --add-flags "$out/lib/node_modules/freebuff/index.js"
+
+    runHook postInstall
+  '';
+
+  doCheck = false;
+
+  passthru = {
+    category = "AI Coding Agents";
+    updateScript = [
+      "nix-update"
+      "--flake"
+      ".#freebuff"
+    ];
+  };
+
+  meta = with lib; {
+    description = "The world's strongest free coding agent";
+    homepage = "https://codebuff.com";
+    license = licenses.mit;
+    mainProgram = "freebuff";
+    platforms = platforms.all;
+  };
+}