docs(core): enhance useFragment JSDoc with examples for type-safe access

[guendev]

…nd complete data usage

[Copilot]

Pull Request Overview

This PR enhances the JSDoc documentation for the useFragment composable by adding comprehensive examples demonstrating type-safe data access patterns. The changes focus on improving developer experience by showing how to properly handle partial data and leverage TypeScript type narrowing.

Key Changes:

• Added examples showing both basic usage with optional chaining and recommended type-safe patterns
• Expanded documentation for the data property with practical examples including a reusable helper pattern
• Enhanced result property documentation with examples for complete/partial data handling

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