arch: extract LoadingButton wrapper; revert vendored button.tsx loading patch

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Problem

The coss-vendored Button in packages/ui/src/components/button.tsx has been hand-modified to add loading-state behavior:

• Imports @vibest/ui/components/spinner
• Adds data-loading variant classes and a loading indicator slot
• Exposes a loading prop

Per ADR 0001, edits inside packages/ui/src/components/* are discarded on registry refresh.

Why it matters

Loading behavior will silently disappear or merge-conflict on the next @coss/ui --overwrite pull.

Suggested fix

Extract a thin LoadingButton wrapper in packages/ui/src/ai-elements/loading-button.tsx that composes vendored Button + Spinner. Revert button.tsx to the registry version.

Affected files

• packages/ui/src/components/button.tsx

Severity

P3