update to nixvim scala metals and copilot configs

programs/nixvim/plugins/ai.nix

@@ -4,14 +4,33 @@
   programs.nixvim = {
     plugins = {
       # GitHub Copilot
-      copilot-vim.enable = true;
+      copilot-vim = {
+        enable = true;
+      };
 
       # Avante AI assistant (imported from separate file)
       # avante config is in avante.nix
     };
 
     globals = {
-      copilot_node_command = lib.mkForce "${pkgs.nodejs-slim}/bin/node";
+      copilot_node_command = lib.mkForce "${pkgs.nodejs}/bin/node";
+      copilot_no_tab_map = true;
+      copilot_assume_mapped = true;
     };
+
+    # Copilot keymapping - use Ctrl+J to accept suggestion
+    keymaps = [
+      {
+        mode = "i";
+        key = "<C-J>";
+        action = "copilot#Accept(\"\\<CR>\")";
+        options = {
+          silent = true;
+          script = true;
+          expr = true;
+          replace_keycodes = false;
+        };
+      }
+    ];
   };
-}
+}