refactor: reorganize, add package (opencode, osgrep, beads), add ai agent shell

packages/opencode.nix

@@ -0,0 +1,59 @@
+{ lib, stdenv, fetchzip, autoPatchelfHook }:
+let
+  version = "1.0.137";
+
+  platformInfo = {
+    x86_64-darwin = {
+      name = "darwin-x64";
+      ext = "zip";
+      hash = "sha256-ZgzvpW8SAN0HP3Qh+aT1S+WrEoXkTZiL8/8z1w9p9Y0=";
+    };
+    aarch64-darwin = {
+      name = "darwin-arm64";
+      ext = "zip";
+      hash = "sha256-w5hs5arVroLtjr9pRAHYXQL+4L5gw1bJVL4DhgvrpLs=";
+    };
+    x86_64-linux = {
+      name = "linux-x64";
+      ext = "tar.gz";
+      hash = "sha256-N8IR3xq/dGF5jPq9/UW8Mu/PnAUb7r+Ox6nge6wKw1M=";
+    };
+    aarch64-linux = {
+      name = "linux-arm64";
+      ext = "tar.gz";
+      hash = "sha256-LwWbTAVnfEmCjUBNf58bgFFVVvDIQVJkLsGtYX+/EfU=";
+    };
+  };
+
+  platform = platformInfo.${stdenv.hostPlatform.system} or (throw
+    "Unsupported system: ${stdenv.hostPlatform.system}");
+in stdenv.mkDerivation {
+  pname = "opencode";
+  inherit version;
+
+  src = fetchzip {
+    url =
+      "https://github.com/sst/opencode/releases/download/v${version}/opencode-${platform.name}.${platform.ext}";
+    hash = platform.hash;
+    stripRoot = false;
+  };
+
+  nativeBuildInputs = lib.optionals stdenv.isLinux [ autoPatchelfHook ];
+
+  installPhase = ''
+    runHook preInstall
+    mkdir -p $out/bin
+    cp opencode $out/bin/opencode
+    chmod +x $out/bin/opencode
+    runHook postInstall
+  '';
+
+  meta = {
+    description = "AI coding assistant CLI from SST";
+    homepage = "https://opencode.ai";
+    license = lib.licenses.mit;
+    mainProgram = "opencode";
+    platforms =
+      [ "x86_64-darwin" "aarch64-darwin" "x86_64-linux" "aarch64-linux" ];
+  };
+}