feat(x-model): add .change, .blur, and .enter event modifiers

[calebporzio]

Overview

By default, x-model syncs on every keystroke (input event). The existing .lazy modifier delays sync until change, but there's no way to sync on blur or Enter keypress.

This PR adds three new event modifiers that give you fine-grained control over when x-model syncs:

Modifier	Syncs when...
.change	Input loses focus after value changed (alias for .lazy)
.blur	Input loses focus
.enter	User presses Enter

Combining modifiers

These modifiers can be combined to sync on multiple events:

<!-- Sync on blur OR Enter -->
<input x-model.blur.enter="search">

<!-- Sync on change, blur, OR Enter -->
<input x-model.change.blur.enter="message">

Use cases

• Search fields: Use .enter to only search when user presses Enter
• Form validation: Use .blur to validate when user leaves a field
• Performance: Use .change to reduce reactivity on large forms

Notes

• .enter does NOT prevent default behavior (forms still submit)
• .lazy remains supported as an alias for .change
• Default x-model behavior is unchanged