Update devman version to 0.2.0 in flake.nix

Sync flake.nix version with pyproject.toml to match version 0.2.0.
This forces Nix to create a new derivation, bypassing cached builds
that were missing the tomli_w dependency.

Author: claude

flake.nix

@@ -27,7 +27,7 @@
         in
         python.pkgs.buildPythonApplication {
           pname = "devman";
-          version = "0.1.1";
+          version = "0.2.0";
           format = "pyproject";
           src = ./.;