docs: clarify confirm dismissal and modal lifecycle in README

[okyrychenko-dev]

Summary

• Put the choice between confirm, custom modals, registry, and renderer near the top.
• Clarify that built-in Cancel and Escape resolve with a typed result, while programmatic dismissal, closeAll, and provider teardown reject.
• Add examples for handling ModalDismissError, caller unmount cleanup, once-only settlement, Strict Mode, and the renderer seam.
• Move the competitor comparison below the usage guides.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-02T06:13:48.443481Z	b08f586	New commits

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Reviewed commit: 5c46e3d0b9

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