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/default/default.nix

@@ -0,0 +1,19 @@
+{
+  pkgs,
+  perSystem,
+  ...
+}:
+let
+  allPackages = perSystem.self;
+
+  # Filter to visible, runnable packages
+  visibleNames = builtins.filter (
+    name: name != "default" && !(allPackages.${name}.passthru.hideFromDocs or false)
+  ) (builtins.attrNames allPackages);
+
+  # Build "name\tdescription" lines
+  packageLines = map (name: "${name}\t${allPackages.${name}.meta.description or ""}") visibleNames;
+
+  packageList = builtins.concatStringsSep "\n" packageLines;
+in
+pkgs.callPackage ./package.nix { inherit packageList; }