Add TypeScript types to submodule exports

[Copilot]

Submodule imports (open-props/src/animations, open-props/src/colors, etc.) lack TypeScript type definitions in their export mappings, causing type resolution failures.

Changes

• package.json: Convert submodule exports from string paths to conditional exports with explicit types field
• tsconfig.json: Add src/index.js to include array for type generation
• gen:types script: Clean existing .d.ts files before regeneration to avoid TS5055 overwrite errors
• tests: Add verification that all submodule type definitions are generated

Usage

import Animations from 'open-props/src/animations';
import Colors from 'open-props/src/colors';

// Types now properly resolve
const fadeIn: string = Animations['--animation-fade-in'];
const gray0: string = Colors['--gray-0'];

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