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/librusty_v8.nix

@@ -0,0 +1,13 @@
+# Pre-built librusty_v8 library for goose-cli
+# This file specifies the rusty_v8 version and hashes for all supported platforms
+{ fetchLibrustyV8 }:
+
+fetchLibrustyV8 {
+  version = "145.0.0";
+  shas = {
+    x86_64-linux = "sha256-chV1PAx40UH3Ute5k3lLrgfhih39Rm3KqE+mTna6ysE=";
+    aarch64-linux = "sha256-4IivYskhUSsMLZY97+g23UtUYh4p5jk7CzhMbMyqXyY=";
+    x86_64-darwin = "sha256-1jUuC+z7saQfPYILNyRJanD4+zOOhXU2ac/LFoytwho=";
+    aarch64-darwin = "sha256-yHa1eydVCrfYGgrZANbzgmmf25p7ui1VMas2A7BhG6k=";
+  };
+}