[Toolkit][Shadcn] Add attachment recipe

[ker0x]

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

Adds the attachment recipe to the Shadcn kit, porting Shadcn's Attachment component: a file or image attachment with media, metadata, upload state and actions.

It ships the root component plus Media, Content, Title, Description, Actions, Action, Trigger and Group sub-components. No Stimulus controller — the component is purely presentational upstream.

<twig:Attachment state="uploading">
    <twig:Attachment:Media>
        <twig:Spinner />
    </twig:Attachment:Media>
    <twig:Attachment:Content>
        <twig:Attachment:Title>sales-dashboard.pdf</twig:Attachment:Title>
        <twig:Attachment:Description>Uploading · 64%</twig:Attachment:Description>
    </twig:Attachment:Content>
    <twig:Attachment:Actions>
        <twig:Attachment:Action aria-label="Cancel upload">
            <twig:ux:icon name="lucide:x" />
        </twig:Attachment:Action>
    </twig:Attachment:Actions>
</twig:Attachment>

All 6 upstream examples are reused as live-preview blocks in the recipe README.md (hero, Image, States, Sizes, Group, Trigger), plus the RTL section.

Notes for reviewers

Upstream paths moved. apps/v4/styles/radix-nova/ui/ no longer exists and ui-rtl/ is gone entirely. Classes here come from registry/new-york-v4/ui/attachment.tsx, which I verified is the flattened equivalent of registry/bases/radix/ui/attachment.tsx plus its cn-attachment* classes expanded from registry/styles/style-nova.css.

Three upstream utilities are substituted. shimmer, scroll-fade-x and scrollbar-none are defined in packages/shadcn/src/tailwind.css, which the kit does not ship — the kit pins shadcn/dist/tailwind.css 4.6.0, which defines none of the three. Following the scroll-area precedent of substituting stock Tailwind:

Upstream	Here	Why
scrollbar-none	no-scrollbar	The pinned 4.6.0 baseline does define this one
shimmer	animate-pulse on the title while uploading/processing	The original needs @property, @keyframes and background-clip: text
scroll-fade-x	omitted	The scroll-driven original needs keyframes absent from the baseline; a static mask would clip the edge cards when unscrolled

Happy to revisit if you'd rather bump the pinned shadcn CSS package instead — that's a kit-wide change so I kept it out of this PR.

Attachment:Trigger takes an as prop (like Button and Item) rather than exposing an attachment_trigger_attrs bag, since it carries no behaviour of its own — it is a positioned overlay. It composes with Dialog:Trigger as <twig:Attachment:Trigger {{ ...dialog_trigger_attrs }} />, which the Trigger example exercises. type="button" is only emitted when it actually renders a <button>.

Also adds 5 lucide icon fixtures (file-code, file-search, file-text, file-warning, table) needed by the examples.

Checks

• bin/ux-toolkit-kit-lint --fail-on-warning kits/shadcn clean
• twig-cs-fixer, oxfmt --check, php-cs-fixer check clean
• Snapshots regenerated and committed; no orphans
• Full Toolkit suite green apart from a pre-existing common/post-link snapshot failure (an attribute-quoting difference on PHP 8.5, fails identically on a clean 3.x)