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/default.nix

@@ -0,0 +1,9 @@
+{
+  pkgs,
+  ...
+}:
+pkgs.callPackage ./package.nix {
+  librusty_v8 = pkgs.callPackage ./librusty_v8.nix {
+    inherit (pkgs.callPackage ./fetchers.nix { }) fetchLibrustyV8;
+  };
+}