docs: add Dialog slide animation example

[totally-not-ai]

Summary

This adds an example to the Dialog styling page. It shows how to make a dialog slide up a little and fade in when it opens, then slide down and fade out when it closes.

What changed

Docs only. No code or behavior changes.

In articles/components/dialog/styling.adoc, after the overlay animation properties:

• Aura / base styles: a short CSS example for dialogs with the slide-in class name. It sets --vaadin-overlay-translate-closed: 0 2rem and --vaadin-overlay-scale-closed: 1, so the dialog slides instead of scaling. The theme still controls the timing.
• Lumo: Lumo has its own Dialog animation, so the properties above do nothing there. The example replaces the opening and closing overlay animations with keyframes that add a slide to the usual fade. It keeps Lumo's built-in durations, delays, and easing, so the dialog still matches the backdrop fade and is removed at the right time.

[github-actions]

Preview Deployment

This PR has been deployed for preview.

URL: https://docs-preview-pr-6187.fly.dev

Changed pages

Added content is highlighted in green; removed content is marked in red on each page.

• components/dialog/styling — modified, +37/-0 lines

Built from 9287a15

[sissbruecker]

@totally-not-ai Extract the dialogs / popovers guide and browser access changes into a separate PR.

[totally-not-ai]

@sissbruecker Done. The dialog keyboard shortcuts section (Add Dialogs & Popovers guide) and the selective printing snippet (Browser Access) are now in their own PR, #6236, and I removed them from this one.

[sissbruecker]

@totally-not-ai

Drop the combo box progress bar and text area examples. These are either too arbitrary, promote bad practices or have broken UX.

For the dialog animation:

• Don't make the dialog move over the whole screen.
• Make the Lumo animation not look broken. The current timing doesn't match the built-in animation. Also overriding the animation removes the built-in opacity animation that Lumo has.

[totally-not-ai]

@sissbruecker Thanks for the review. I removed the Combo Box, Progress Bar, and Text Area examples, so this PR now only contains the Dialog animation. Changes to it:

• The dialog now slides a short distance (2rem) instead of across the whole viewport.
• In Aura, only --vaadin-overlay-translate-closed and --vaadin-overlay-scale-closed are set, so the theme's own durations, delay, and opacity fade still apply.
• In Lumo, the opening and closing keyframes keep the built-in opacity fade and add the slide in place of the scale. They use the same durations, delays, and easing curves as Lumo's vaadin-dialog-enter / vaadin-dialog-exit (0.12s after 0.05s, and 0.1s after 0.03s), so they stay in sync with the backdrop and finish within the 0.25s Lumo waits before removing the dialog.