feat(ebook-search): update test workflow to use nix for dependency management

shell.nix

@@ -3,6 +3,20 @@
   ...
 }:
 {
+  # For running the uv-managed ebook-search venv outside the container:
+  # PyPI manylinux wheels (numpy via bm25s) expect libstdc++.so.6 on the
+  # loader path, which NixOS does not provide globally.
+  ebook-search = pkgs.mkShell {
+    nativeBuildInputs = with pkgs; [
+      my_python
+      uv
+    ];
+    LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [
+      pkgs.stdenv.cc.cc.lib
+      pkgs.zlib
+    ];
+  };
+
   default = pkgs.mkShell {
     NIX_CONFIG = "extra-experimental-features = nix-command flakes ca-derivations";
     nativeBuildInputs = with pkgs; [