fix: use correct Datastar keydown event syntax

Replace invalid .key_enter and .enter modifiers with evt.key === 'Enter'
guard in the expression, per Datastar docs. Also fix __stop and __throttle
modifier syntax to use double underscores.

features/common/components/shared.templ

@@ -28,7 +28,7 @@ templ NicknamePrompt(returnPath string) {
 					type="text"
 					placeholder="Enter your nickname"
 					data-bind="nickname"
-					data-on:keydown.key_enter={ datastar.PostSSE("%s", returnPath) }
+					data-on:keydown={ "evt.key === 'Enter' && " + datastar.PostSSE("%s", returnPath) }
 					required
 					autofocus
 				/>