feat: add abort/cancel support for confirmations

[haradakunihiko]

Summary

Add external cancellation (abort) support for confirmation dialogs.

• Supports AbortController-based cancellation (recommended)
• Adds utility functions abort(promise) and abortAll()
• When aborted, the Promise rejects with AbortError and the UI unmounts automatically
• createConfirmation now accepts an optional second argument { signal?: AbortSignal }

Changes

• New: src/controls.ts
  • Lightweight registry to track pending confirmations and cancel them
  • Exposes abort(promise), abortAll(), and attachAbortSignal
• Update: src/createConfirmation.ts
  • Registers created Promises and ensures reject + unmount on cancellation
  • Accepts control?: { signal?: AbortSignal } and wires the signal
• Types: src/types.ts
  • Reflects control?: { signal?: AbortSignal } in ConfirmationContext#createConfirmation
• Exports: src/index.ts
  • Exposes abort and abortAll
• Docs: README.md
  • Adds a "Cancellation (Abort)" section
• Tests: __tests__/abort.test.js
  • Covers single abort, abortAll for multiple, and AbortSignal-driven cancellation

Usage

• Using AbortController (recommended)

const confirm = createConfirmation(confirmable(MyDialog));
const ac = new AbortController();
const p = confirm({ message: 'Delete?' }, { signal: ac.signal });
// Later
ac.abort(); // p rejects with AbortError and the dialog closes

• Using utility functions

const confirm = createConfirmation(confirmable(MyDialog));
const p = confirm({ message: 'Delete?' });
abort(p);     // cancel one
abortAll();   // cancel all pending

Compatibility

• Existing calls createConfirmation(props) continue to work; the second parameter is optional.
• Aborted promises reject with an error whose name === 'AbortError'. If your app relies on specific error types, please handle accordingly.

Tests

• Adds JSDOM-based unit tests. Verified locally with npm test.

If you want additional docs (screenshots, migration notes, etc.), I can add them.