Add quote and attribution editors in the inspector

## Summary
`quote-full` layout has quote + attribution slots. Inspector treats them as generic textareas without context.

## Tasks
- [ ] Group quote + attribution fields visually
- [ ] Add character limits from slot `maxLength`
- [ ] Style preview hints (italic quote block)

## Files
- `apps/web/app/editor/[id]/Editor.tsx`
- `layouts/quote-full/slide.config.ts`

Start in apps/web/app/editor/[id]/Editor.tsx to trace how quote-full fields are rendered in the inspector, then read layouts/quote-full/slide.config.ts for the quote and attribution slots and their maxLength values. Done means the fields are visually grouped, character limits are shown, and the preview hints style the quote as an italic block.

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