Add support for IDML (InDesign Markup Language) file format

[vrcprl]

What

Implement a loader for IDML files in Replexica.

Why

To support designers and print publishers working with magazine layouts and brochures.

How

1. Create a new loader in packages/cli/src/loaders/idml.ts
2. Implement parsing logic for IDML XML structure
3. Add two unit tests in packages/cli/src/loaders/index.spec.ts:
   • Test parsing a simple IDML file
   • Test handling style ranges in IDML entries
4. Update @replexica/spec to include IDML format
5. Generate a changeset using pnpm new for both 'replexica' and '@replexica/cli' packages
6. In the pull request, include a link to the IDML specification used.

After completing the task

Noticed a file format Replexica doesn't yet support? Please create a new GitHub ticket (if it doesn't yet exist!), using the format/structure of this GitHub issue.