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/fetchers.nix

@@ -0,0 +1,21 @@
+# Fetchers for goose-cli pre-built dependencies
+# Based on deno's approach for handling rusty_v8
+{
+  lib,
+  stdenv,
+  fetchurl,
+}:
+
+{
+  fetchLibrustyV8 =
+    args:
+    fetchurl {
+      name = "librusty_v8-${args.version}";
+      url = "https://github.com/denoland/rusty_v8/releases/download/v${args.version}/librusty_v8_release_${stdenv.hostPlatform.rust.rustcTarget}.a.gz";
+      sha256 = args.shas.${stdenv.hostPlatform.system};
+      meta = {
+        inherit (args) version;
+        sourceProvenance = with lib.sourceTypes; [ binaryNativeCode ];
+      };
+    };
+}