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; }

packages/default/package.nix

@@ -0,0 +1,60 @@
+{
+  lib,
+  writeShellApplication,
+  fzf,
+  nix,
+  util-linux,
+  packageList,
+}:
+
+let
+  packageListFile = builtins.toFile "millerson-overlay-packages.tsv" packageList;
+in
+writeShellApplication {
+  name = "millerson-overlay-launcher";
+
+  runtimeInputs = [
+    fzf
+    nix
+    util-linux # column
+  ];
+
+  text = ''
+    # Format for fzf: "name  description" (tab-aligned)
+    entries=$(column -t -s $'\t' < "${packageListFile}")
+
+    if [[ -z $entries ]]; then
+      echo "No packages found" >&2
+      exit 1
+    fi
+
+    # Let user pick with fzf
+    selected=$(echo "$entries" | fzf \
+      --header="Select an pkg to run (ESC to cancel)" \
+      --preview-window=hidden \
+      --no-multi \
+      --height=~40% \
+      --layout=reverse) || exit 0
+
+    # Extract package name (first word)
+    pkg_name=$(echo "$selected" | awk '{print $1}')
+
+    if [[ -z $pkg_name ]]; then
+      exit 0
+    fi
+
+    echo "→ Running: nix run git.millerson.name/alex/nix-overlay.git#$pkg_name"
+    exec nix run "git.millerson.name/alex/nix-overlay.git#$pkg_name"
+  '';
+
+  meta = with lib; {
+    description = "Interactive fzf launcher for millerson-overlay.nix packages";
+    license = licenses.mit;
+    mainProgram = "millerson-overlay-launcher";
+    platforms = platforms.all;
+  };
+
+  passthru = {
+    hideFromDocs = true;
+  };
+}