docs(examples): add demo with multiple validation libs

[CorentinTh]

No description provided.

[Copilot]

Pull Request Overview

This PR adds a new demo file showcasing how figue can work with multiple validation libraries (Zod, Valibot, and custom Standard Schema implementations) to demonstrate its flexibility in handling different schema types. The README is also updated to highlight that figue has no runtime dependencies.

• Adds a comprehensive demo showing interoperability with multiple validation libraries
• Updates README to emphasize the zero runtime dependencies feature

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
demo/figue-mix.ts	New demo file demonstrating mixed validation library usage with Zod, Valibot, and custom Standard Schema
README.md	Added feature bullet point about no runtime dependencies

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