Add devenv to project

- Init devenv with node22 and corepack22
- Add devenv gitignore
- Direnv auto active devenv shell
- Update pnpm corepack version to 10.25.0
- Rerun pnpm install

Signed-off-by: Asai Neko <sugar@sne.moe>

devenv.nix

@@ -0,0 +1,12 @@
+{ pkgs, ...}:
+
+{
+  env.GREET = "devenv";
+
+  packages = [
+      pkgs.git
+      pkgs.nodejs_22
+      pkgs.corepack_22
+      pkgs.typescript-language-server
+  ];
+}