- Add is_stackable field to AddOnProduct model for add-ons that can be
purchased multiple times
- Add quantity field to SubscriptionAddOn for tracking purchase count
- Update EntitlementService to ADD integer add-on values to base plan
(instead of max) and multiply by quantity for stackable add-ons
- Add feature selection to AddOnEditorModal using FeaturePicker component
- Add AddOnFeatureSerializer for nested feature CRUD on add-ons
- Fix Create Add-on button styling to use solid blue (was muted outline)
- Widen billing sidebar from 320px to 384px to prevent text wrapping
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
