Initialize Nix overlay repository with blueprint, goose-cli, and docs

Add the complete overlay structure using numtide/blueprint with:
- Two overlay strategies (default and shared-nixpkgs)
- goose-cli package with custom librusty_v8 fetcher
- Interactive package launcher via fzf
- Flake input caching utility
- Comprehensive README and AGENTS.md documentation

packages/goose-cli/package.nix

@@ -0,0 +1,71 @@
+{
+  lib,
+  fetchFromGitHub,
+  rustPlatform,
+  pkg-config,
+  openssl,
+  libxcb,
+  dbus,
+  versionCheckHook,
+  librusty_v8,
+}:
+
+rustPlatform.buildRustPackage rec {
+  pname = "goose-cli";
+  version = "1.33.1";
+
+  src = fetchFromGitHub {
+    owner = "block";
+    repo = "goose";
+    rev = "v${version}";
+    hash = "sha256-FBICGOfVs2jbOdLWSInqfTYBdnCcbcGWHwqY/b6v8eg=";
+  };
+
+  cargoHash = "sha256-fN0FKDYFkZrQQPWdUlemOaGzIAZhqFyskz9TEmG+X4o=";
+
+  nativeBuildInputs = [ pkg-config ];
+
+  buildInputs = [
+    openssl
+    libxcb
+    dbus
+  ];
+
+  # The v8 package will try to download a `librusty_v8.a` release at build time to our read-only filesystem
+  # To avoid this we pre-download the file and export it via RUSTY_V8_ARCHIVE
+  env.RUSTY_V8_ARCHIVE = librusty_v8;
+
+  # Build only the CLI package
+  cargoBuildFlags = [
+    "--package"
+    "goose-cli"
+  ];
+
+  # Enable tests with proper environment
+  doCheck = true;
+  checkPhase = ''
+    export HOME=$(mktemp -d)
+    export XDG_CONFIG_HOME=$HOME/.config
+    export XDG_DATA_HOME=$HOME/.local/share
+    export XDG_STATE_HOME=$HOME/.local/state
+    export XDG_CACHE_HOME=$HOME/.cache
+    mkdir -p $XDG_CONFIG_HOME $XDG_DATA_HOME $XDG_STATE_HOME $XDG_CACHE_HOME
+
+    # Run tests for goose-cli package only
+    cargo test --package goose-cli --release
+  '';
+
+  doInstallCheck = true;
+  nativeInstallCheckInputs = [ versionCheckHook ];
+
+  passthru.category = "AI Coding Agents";
+
+  meta = with lib; {
+    description = "CLI for Goose - a local, extensible, open source AI agent that automates engineering tasks";
+    homepage = "https://github.com/block/goose";
+    changelog = "https://github.com/block/goose/releases/tag/v${version}";
+    license = licenses.asl20;
+    sourceProvenance = with sourceTypes; [ fromSource ];
+    mainProgram = "goose";
+  };
+}