Allow different `outputRoots` per `target`

[jan-ladleif]

Current behaviour

The output root of rulesync is configurable via the config file, e.g.,

  "outputRoots": [
    "build"
  ],

However, outputs for all targets are placed top-level in build/ and there is no distinction between the target platforms.

Feature request

For bundling my project for different targets cleanly, I would love to have the ability to specify an output root for each target, e.g.,

  "outputRoots": {
    "copilot": "build/copilot",
    "claudecode": "build/claudecode",
    ...
  },

This way, each target platform would get a clean, easily distributable, self-contained folder.