refactor(selector): not hiding the first option HTML element anymore

[mfranzke]

Proposed changes

• it's inconsistent in between browsers (Safari would still display that option[hidden])
• it's inconsistent and incorrect for regular select-HTML-elements, as those would actually mark the first option as checked as well, whereas this is actually the selected one (gets transmitted in form submits etc.)
• In case that somebody would like to use floating labels or placeholder, there should be an option that the users could set to "unselect" all selectable options, or in other words "reset" any other selection. We wouldn't provide this possibility at the moment anyhow.

Resolves #4019

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (fix on existing components or architectural decisions)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Further comments

[github-actions]

🔭🐙🐈 Test this branch here: https://db-ux-design-system.github.io/core-web/review/4019-dbselect-dropdown-checkmark-on-first-element

[Copilot]

Pull Request Overview

This PR refactors the select component to improve browser consistency and form behavior by replacing the hidden placeholder option with a visible CSS-classed option. The changes address Safari-specific display issues and ensure the select component behaves like standard HTML select elements.

Key Changes:

• Replace hidden attribute with .placeholder CSS class for the first option element
• Update CSS selectors to target .placeholder class instead of [hidden] attribute
• Add placeholder props to showcase examples and tests

Reviewed Changes

Copilot reviewed 18 out of 22 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/components/src/components/select/select.lite.tsx	Core component logic updated to use CSS class instead of hidden attribute for placeholder option
packages/components/src/styles/internal/_form-components.scss	Updated CSS selector from [hidden] to .placeholder class
packages/components/src/components/select/select.scss	Updated CSS selector for placeholder option styling
showcases/shared/select.json	Added placeholder properties to all showcase examples
showcases/vue-showcase/src/components/select/Select.vue	Fixed placeholder prop binding from exampleName to exampleProps?.placeholder
showcases/react-showcase/src/components/select/index.tsx	Updated prop name from children to placeholder
packages/components/src/components/select/index.html	Updated HTML examples to use CSS class instead of hidden attribute
packages/components/src/components/select/select.spec.tsx	Added value prop to test component
Multiple snapshot files	Updated accessibility snapshots to reflect new option structure

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[Copilot]

The condition props.placeholder !== '' will show the placeholder span even when props.placeholder is undefined or null. This should check for truthy values: <Show when={props.placeholder}> to properly handle all falsy cases.

Suggested change

	<Show when={props.placeholder !== ''}>
	<Show when={props.placeholder}>