feat(neovim): migrate to nixvim with minimal plugins (#260)

Replace bare programs.neovim with programs.nixvim. Only 3 plugins:
neo-tree (file explorer), catppuccin (colorscheme), treesitter.

Add core editor opts matching helix defaults: clipboard, cursorline,
scrolloff, wrap, mouse, undofile, smart search, split direction.
Enable 5 LSP servers: nixd, rust-analyzer, gopls, pyright, bashls.

Signed-off-by: Ryan Yin <xiaoyin_c@qq.com>

home/base/core/editors/neovim/default.nix

@@ -1,14 +1,96 @@
-{ pkgs, ... }:
+{ config, nixvim, ... }:
 {
-  programs = {
-    neovim = {
+
+  imports = [ nixvim.homeModules.nixvim ];
+  home.shellAliases = {
+
+    vi = "nvim";
+    vim = "nvim";
+  };
+
+  programs.nixvim = {
+    enable = true;
+
+    clipboard.providers.wl-copy.enable = true;
+
+    opts = {
+      number = true;
+      relativenumber = true;
+      cursorline = true;
+      signcolumn = "auto";
+      clipboard = "unnamedplus";
+      scrolloff = 8;
+      swapfile = false;
+      title = true;
+      titlelen = 20;
+      smartindent = false;
+      mouse = "a";
+      undofile = true;
+      ignorecase = true;
+      smartcase = true;
+      splitbelow = true;
+      splitright = true;
+      updatetime = 300;
+      wrap = true;
+      linebreak = true;
+    };
+
+    colorschemes.catppuccin = {
       enable = true;
+      settings = {
+        transparent_background = true;
+      };
+    };
 
-      viAlias = true;
-      vimAlias = true;
+    plugins.lsp.servers = {
+      nixd.enable = true;
+      "rust_analyzer" = {
+        enable = true;
+        installCargo = false;
+        installRustc = false;
+      };
+      gopls.enable = true;
+      pyright.enable = true;
+      bashls.enable = true;
+    };
 
-      withRuby = false;
-      withPython3 = false;
+    plugins.treesitter = {
+      enable = true;
+      grammarPackages = with config.programs.nixvim.plugins.treesitter.package.builtGrammars; [
+        bash
+        json
+        lua
+        make
+        markdown
+        nix
+        regex
+        rust
+        go
+        python
+        toml
+        vim
+        vimdoc
+        xml
+        yaml
+        nu
+      ];
+    };
+
+    plugins.neo-tree = {
+      enable = true;
+      settings = {
+        filesystem = {
+          filtered_items = {
+            visible = true;
+            hide_dotfiles = false;
+            hide_gitignored = false;
+          };
+          follow_current_file = {
+            enabled = true;
+            leave_dirs_open = false;
+          };
+        };
+      };
     };
   };
 }