[Toolkit][Shadcn] Add popover recipe

[Amoifr]

Q	A
Bug fix?	no
New feature?	yes
Deprecations?	no
Documentation?	no
Issues	Part of #3233
License	MIT

Adds the popover recipe to the Shadcn kit.

Part of the split of #3468 into one PR per component, tracking #3233.

Snapshots will be regenerated after rework.

[Amoifr]

Main example

Capture.video.du.2026-04-20.08-41-21.mp4

[Amoifr]

Basic example

Capture.video.du.2026-04-20.08-42-25.mp4

[Amoifr]

Align example

Capture.video.du.2026-04-20.08-47-25.mp4

[Amoifr]

With form example

Capture.video.du.2026-04-20.08-53-15.mp4

[Amoifr]

RTL example

Capture.video.du.2026-04-20.09-01-46.mp4

[Kocal]

By doing this, you are forcing the user to use a button like as a trigger, this is not our philosophy.

Please check the existing *Trigger.html.twig, they are nearly-empty templates that expose a Twig variable ..._trigger_attrs, e.g. with AlertDialog/Trigger.html.twig:

{# @block content The trigger element (e.g., a `Button`) that opens the dialog when clicked #}
{%- set alert_dialog_trigger_attrs = {
    'data-action': 'click->alert-dialog#open'|html_attr_type('sst'),
    'data-alert-dialog-target': 'trigger',
    'aria-haspopup': 'dialog',
    'aria-expanded': 'false',
} -%}
{%- block content %}{% endblock -%}

Usage:

<twig:AlertDialog id="delete_account">
    <twig:AlertDialog:Trigger>
        <twig:Button variant="outline" {{ ...alert_dialog_trigger_attrs }}>
            Show Dialog
        </twig:Button>
    </twig:AlertDialog:Trigger>
    <twig:AlertDialog:Content>...</twig:AlertDialog:Content>
</twig:AlertDialog>

It also means that you must not use details and summary HTML elements.

Thanks!

[Amoifr]

Reworked to apply the _trigger_attrs convention (from your review on this very PR): swapped native <details>/<summary> for a <div> + a small Stimulus controller so the Trigger stays element-agnostic. Moving back to draft so you can re-test at your convenience. Thanks for the patience! 🙏

[Amoifr]

Re-tested locally on ux.symfony.com (with the matching controller registration on symfony/ux.symfony.com#70) — open/close, outside click and escape all behave as expected on every example (Demo / Usage / Basic / Alignments / Form / RTL). Back to ready for review. 🙌