CSS: add GradientColorStripSource with visual editor
- Backend: GradientColorStripSource storage model, GradientColorStripStream
with numpy interpolation (bidirectional stops, auto-size from device LED count),
ColorStop Pydantic schema, API create/update/guard routes
- Frontend: gradient editor modal (canvas preview, draggable markers, stop rows),
CSS hard-edge card swatch, locale keys (en + ru)
- Fixes: stop row mousedown no longer rebuilds DOM (buttons now clickable),
position input max-width, bidir/remove button static width
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
alexei.dolgolyov
7479b1fb8d