Add support for Factory's Droid AI assistant, allowing users to install
the skill via 'uipro init --ai droid' to .factory/skills/ directory.
Changes:
- Add droid.json platform config (src and cli/assets)
- Add 'droid' to AIType and AI_TYPES array
- Add .factory directory detection
- Add droid to AI_TO_PLATFORM mapping
Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>