neovim: let nixd resolve nixpkgs for hover / go-to-definition

[etrobert-bot]

Goal

Make the nixd LSP resolve symbols from nixpkgs so hover and go-to-definition work on pkgs.* references (e.g. hovering pkgs.ripgrep or jumping into a package definition).

Background

pkgs/neovim-wrapped/plugins/lspconfig/config.lua configures nixd with settings.nixd.options (nixos/darwin option sets) but no settings.nixd.nixpkgs.expr. Per nixd's configuration, nixpkgs.expr provides the package set nixd evaluates for completion/hover/definition on pkgs.*; without it nixd has no nixpkgs data. (nixd docs: docs/configuration.md, key nixpkgs.expr, default import <nixpkgs> { }.)

Plan

• Add a nixpkgs block alongside the existing options block in the nixd settings:

  nixpkgs = {
    expr = "import (builtins.getFlake (builtins.toString ./.)).inputs.nixpkgs { }",
  },

  This reuses the flake's own nixpkgs input rather than a <nixpkgs> channel lookup, consistent with the existing options.*.expr values and with the repo's flake-native Nix style (no <nixpkgs>).

Verification

• nix build .#neovim-wrapped succeeds.
• Lua config remains syntactically valid (loads in headless nvim without error).
• Manual: in a nix file, hover over a pkgs.<name> reference resolves (noted as a manual step; headless LSP hover is hard to assert in CI).

From the linux todo list: "Make is so that nixd can find stuff from the store, for example on hover or go to definition".