feat(nvim): migrate editor from vim to Neovim (parity + LSP)

Rewrite editor.nix on programs.nixvim, keeping every prior feature: file
tree (nvim-tree, toggle ,,), indent guides (indent-blankline), fugitive,
vim-tmux-navigator, Catppuccin Mocha, 2-space hard tabs, and the
*Jenkinsfile=groovy rule. Replace the inert ALE with a real LSP stack —
nvim-lspconfig, nvim-cmp completion, and tree-sitter for highlighting.
Leader is Space; LSP keymaps gd/gr/K/<leader>rn/<leader>ca.

Universal servers: nil (Nix), lua_ls, pyright (Python), terraformls. The
work box (work.nix) additionally enables omnisharp (C#) and helm_ls (Helm),
so the heavy omnisharp closure stays off the personal machines.

default.nix drops VISUAL=vim so nixvim's defaultEditor owns $EDITOR/$VISUAL.
README and KEYBINDINGS updated (and two stale references corrected).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyrathorpe/home/README.md

@@ -10,12 +10,12 @@ Keyboard shortcuts have their own reference: [`KEYBINDINGS.md`](./KEYBINDINGS.md
 | ------------------------------------- | ----------------------------------------------------- |
 | zsh, CLI tools, tmux, ssh, auto-tmux  | [`shell.nix`](./shell.nix)                            |
 | git (+ delta, commitizen)             | [`git.nix`](./git.nix)                                |
-| vim                                   | [`editor.nix`](./editor.nix)                          |
+| Neovim (nixvim) + LSP                 | [`editor.nix`](./editor.nix)                          |
 | GUI apps, GTK/Firefox theming, cursor | [`desktop.nix`](./desktop.nix) (graphical hosts only) |
 
 Shared by every host via [`default.nix`](./default.nix); the work box also layers
-[`../../system/modules/work/default.nix`](../../system/modules/work/default.nix)
-on top (work email, its own ssh config, extra packages).
+[`work.nix`](./work.nix) on top (work email, its own ssh config, extra packages,
+and the C#/Helm language servers).
 
 ---
 
@@ -53,8 +53,9 @@ on top (work email, its own ssh config, extra packages).
 driven from the shared `../catppuccin-mocha.nix` palette / the catppuccin/bat
 theme.
 
-**Env & defaults:** `xdg.enable` on; `PAGER`/`MANPAGER` (bat)/`VISUAL` set in
-`default.nix`; `xdg.mimeApps` maps web→Firefox, directories→nemo (`desktop.nix`).
+**Env & defaults:** `xdg.enable` on; `PAGER`/`MANPAGER` (bat) set in `default.nix`
+(the editor owns `$EDITOR`/`$VISUAL`); `xdg.mimeApps` maps web→Firefox,
+directories→nemo (`desktop.nix`).
 
 ## tmux
 
@@ -90,6 +91,32 @@ Darwin config). foot uses it as its main font automatically. iTerm2's font is a
 GUI setting — set it to _JetBrainsMono Nerd Font_ (Settings → Profiles → Text →
 Font) so the tmux statusline glyphs render instead of `?`.
 
+## Editor (Neovim)
+
+`nvim` — aliased to `vi`/`vim`, and set as `$EDITOR`/`$VISUAL` — is configured
+declaratively with **nixvim**, so the same plugins and config are baked in on
+every host. Migrated from plain vim; the practical gain is a real LSP stack in
+place of the old (inert) ALE.
+
+| Feature       | Notes                                                                                  |
+| ------------- | -------------------------------------------------------------------------------------- |
+| Colorscheme   | Catppuccin Mocha (matches the terminal and the rest of the desktop)                    |
+| File tree     | nvim-tree, toggled with `,,` (comma twice; was nerdtree)                               |
+| Indent guides | indent-blankline, on by default (was vim-indent-guides)                                |
+| Git           | fugitive (`:Git …`)                                                                    |
+| Pane nav      | vim-tmux-navigator — `Ctrl`+`h/j/k/l` moves across vim splits and tmux panes           |
+| Syntax        | tree-sitter (nix, lua, bash, markdown, groovy) — replaces `syntax enable`              |
+| LSP           | nvim-cmp completion + servers `nil` (Nix), `lua_ls`, `pyright` (Python), `terraformls` |
+| Indentation   | 2-wide hard tabs (`noexpandtab`, `tabstop`/`shiftwidth` = 2); line numbers on          |
+| Filetypes     | `*Jenkinsfile` → groovy                                                                |
+
+Leader is `Space`. LSP keymaps (`gd`, `gr`, `K`, `<leader>rn`, `<leader>ca`) and
+the file-tree toggle are listed in
+[`KEYBINDINGS.md`](./KEYBINDINGS.md#neovim). Add a universal language server by
+enabling it under `programs.nixvim.plugins.lsp.servers` in `editor.nix`;
+host-specific ones go in that host's module — the work box (`work.nix`) adds
+`omnisharp` (C#) and `helm_ls` (Helm), kept off the personal machines.
+
 ## git
 
 Pager is **delta**. **commitizen** is installed on every host; `cz` defaults to