Change default task mode to 'before' for better dependency handling

[domenkozar]

Issue

When running a task that has dependencies (via before/after configurations), the dependent tasks don't run by default unless explicitly using --mode before.

Example

Given this configuration:

tasks = {
  "admin:build" = {
    exec = ''
      npm install
      npm run build
    '';
    cwd = "${config.git.root}/services/admin";
    before = [ "admin:deploy" ];
  };
  "admin:deploy" = {
    exec = ''
      some_deploy_command
    '';
    after = [ "admin:build" ];
  };
};

When running devenv tasks run admin:deploy, the build task doesn't run, breaking the deployment.

Workaround: Use devenv tasks run admin:deploy --mode before

Proposed Solution

Change the default task execution mode from the current default to --mode before so that task dependencies are respected by default. This would be more intuitive for users defining task dependencies.

[domenkozar]

A good example is #2589

[pokonski]

Would be good to have this be configurable via devenv.nix, so we can adjust what the default value is

[domenkozar]

I'm not sure it should be configurable per project. Would --mode before not work for you?