feat(nix): migrate Neovim to Nix (as a symlink)

nix/home/neovim/nvim/lua/plugins/copilot-chat.lua

@@ -0,0 +1,13 @@
+-- Chat with GitHub Copilot in Neovim
+-- https://github.com/CopilotC-Nvim/CopilotChat.nvim
+return {
+  {
+    "CopilotC-Nvim/CopilotChat.nvim",
+    branch = "canary",
+    dependencies = {
+      { "zbirenbaum/copilot.lua" }, -- or github/copilot.vim
+      { "nvim-lua/plenary.nvim" }, -- for curl, log wrapper
+    },
+    opts = {},
+  },
+}