Keyboard events: keydown filtering example can't block IME-composed input (Korean/Japanese/Chinese)

Personne n'a encore pris cette issue.

## Article

[Keyboard: keydown and keyup](https://javascript.info/keyboard-events) — the "Default actions" section, phone-number filter example:

```html

```

## Problem

The example (and the surrounding text) implies that returning `false` from `keydown` reliably prevents unwanted characters from being entered. That holds for direct (Latin) keyboard input, but not for languages typed through an IME (Input Method Editor), such as Korean, Japanese and Chinese.

With an IME active:

- `keydown` fires with `event.key == "Process"` (and `keyCode` 229), not the actual character.
- More importantly, calling `preventDefault()` / returning `false` on that `keydown` does **not** cancel the text insertion, because the character is produced by the IME composition, not by the key's default action.

As a result, Korean/Japanese/Chinese characters pass straight through the filter and appear in the field. This was reported by a Korean reader of the Korean translation (ko.javascript.info), and is easy to reproduce by switching to a Korean IME and typing into the demo.

## Suggestion

Add a short note after the example, along these lines:

> Please note: this filter only works for direct keyboard input. Text composed via an IME (used for languages such as Korean, Japanese or Chinese) is inserted by the input method, not by the key's default action, so it can't be blocked in `keydown`. That's one more reason why, for tracking or validating what actually gets into the field, the `input` event is a better choice.

This ties in nicely with the introduction of the article, which already recommends the `input` event for tracking input from any source.

Happy to send a PR if the note sounds good.

Ouvrez l’article Keyboard: keydown and keyup et relisez la section Default actions, en particulier l’exemple de filtre de numéro de téléphone et la présentation de l’input event dans l’introduction. Ajoutez une courte note expliquant la limitation de l’IME et pourquoi input est préférable pour suivre ou valider le texte inséré, puis vérifiez la formulation par rapport à l’exemple.

Rédigé par le modèle d'indexation à partir du texte de l'issue.