DateTimeInput date parsing is not great.

The Date parsing on the DateTimeInput is not super flexible and because of how browsers work, may "clear" values when rendering them.

Our basic catalog implementation should be a little bit more [robust](https://github.com/a2ui-project/a2ui/blob/main/renderers/angular/src/v0_9/catalog/basic/date-time-input.component.ts#L108-L118) [than](https://github.com/a2ui-project/a2ui/blob/main/renderers/lit/src/v0_9/catalogs/basic/components/DateTimeInput.ts#L31-L52) [this](https://github.com/a2ui-project/a2ui/blob/main/renderers/react/src/v0_9/catalog/basic/components/DateTimeInput.tsx#L22-L40).

There's some cool libraries that we could use (like `any-date-parser` backed by Intl?), but as an MVP, we should guarantee that we can parse exactly what the spec says (and add tests to prove it)

The issue points to three component files in different renderers (angular, lit, react) under the v0_9 catalog. Start by examining the linked lines to understand the current date parsing logic. The goal is to make parsing robust per the spec, ensuring it handles browser quirks and doesn't clear values. Write tests to verify the new parsing works exactly as the spec requires.

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