Colmena Module Implementation

1. Defines options under stackpanel.colmena.*
2. Adds colmena to devshell packages
3. Generates wrapper scripts: colmena-apply, colmena-build, colmena-eval
4. Computes resolved flag sets in stackpanel.colmena.computed
5. Registers health checks for CLI availability and hive config

stackpanel.colmena = {
  enable = true;
  flake = ".#colmena";
  parallel = 4;
  buildOnTarget = true;
};