v1.6.0

release 1.6.0: docs, example version, CI

- document positional-argument / remainder handling (options may appear before,
  after or between positionals; `--` ends option parsing)
- bump example + README version strings to 1.6.0
- CI: checkout@v5, push/pull_request triggers, drop the unused submodule step;
  release workflow uses create-release-action@v2 / upload-recursive-asset-action@v2
  (aligned with the splash-drm workflows)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Oskari Rauta <oskari.rauta@gmail.com>