build: migrate to devenv

- Add devenv.nix with Python/uv setup and git-hooks
- Add devenv.yaml and devenv.lock
- Refactor flake.nix to use devenv integration
- Update .envrc from flake to devenv
- Add devenv artifacts to .gitignore

devenv.nix

@@ -0,0 +1,28 @@
+{
+  pkgs,
+  ...
+}:
+{
+  languages = {
+    python = {
+      enable = true;
+      uv.enable = true;
+    };
+  };
+
+  packages = [
+    pkgs.basedpyright
+  ];
+
+  git-hooks.hooks = {
+    basedpyright = {
+      enable = true;
+      entry = "${pkgs.basedpyright}/bin/basedpyright";
+      files = "\\.py$";
+      types = [ "file" ];
+    };
+    ruff.enable = true;
+    ruff-format.enable = true;
+    commitizen.enable = true;
+  };
+}