feat(commerce-onboarding): gate Shopify card behind ?shopify search param

[viktormarinho]

Summary

Hide the Shopify companion card in commerce onboarding (both the blocking connect modal and the /commerce-onboarding route) unless the URL contains a shopify search param (any value: ?shopify, ?shopify=1, …).

The filter lives in useCommerceCompanions, the single point both surfaces build cards from. Filtering the binding requirements up front also means the registry never fetches the Shopify app when the param is absent.

Notes

• Without the param, an already-linked Shopify connection is also hidden (visual only — the connection itself is untouched).
• bun run fmt and tsc --noEmit pass.

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Summary by cubic

Gate the Shopify companion card in commerce onboarding behind a ?shopify search param. The card won’t render or fetch from the registry unless the param is present.

• Use useSearch from @tanstack/react-router to show Shopify only when ?shopify is in the URL.
• Filter companion requirements to skip Shopify when absent, so the registry app isn’t fetched; existing Shopify links remain but are hidden visually.

^{Written for commit 503eeca. Summary will update on new commits.}