fix(settings): don't hide the infra tab while owned-sites is still loading

[pedrofrxncx]

Bug found while reviewing the org-settings tab strip (use-settings-tabs.ts), the same flicker family as #6340.

useVisibleSettingsTabs gates the Billing group's "Infrastructure" tab on requiresOwnedSites, reading useOwnedSites().sites.length > 0 directly. useOwnedSites is a plain useQuery that starts with data undefined, so sites is [] until the request resolves — on every settings page load, an org that actually owns legacy sites momentarily has the tab hidden, then it pops in once the query completes. The capability-gated tabs already avoid this exact flicker via an explicit loading check (see the hook's own doc comment: "Mirrors the sidebar's optimistic-while-loading rule... so owners never see the tab strip flicker") — the owned-sites gate was just never wired into that rule.

Fix: destructure isLoading from useOwnedSites() and don't hide the tab while it's still loading, matching the capabilities gate below it.

Failure scenario: an org that owns a legacy deco.cx site opens Settings → Billing; the "Infrastructure" tab is briefly absent from the tab strip, then appears once INFRA_BILLING_SITES_LIST resolves — a visible layout shift on a page that otherwise (post #6340) is supposed to stay stable while tabs load.

Reviewer check: cd apps/web && bunx tsc --noEmit (green). No test added — this is a plain react-query-derived boolean with no branch worth mocking a query client for; behavior is directly readable from the diff.

Locally ran: bun run fmt, bunx tsc --noEmit (apps/web), bunx oxlint on the changed file — all clean. Full CI (lint, unit, e2e) validates the rest.

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Summary by cubic

Stop hiding the Billing “Infrastructure” tab while owned sites are still loading to eliminate a first-render flicker. Previously the tab was hidden until useOwnedSites resolved (empty array by default); now it stays visible during loading and hides only if the loaded result has no owned sites.

Reviewer notes

• Behavior change: tabs with requiresOwnedSites remain visible while useOwnedSites is loading; they hide only after load confirms no sites, matching the capabilities gate and preventing layout shift on Settings → Billing.
• Validate with an org that owns a legacy site: the tab should not flicker on initial render. No migration or config changes.

^{Written for commit e2b6e31. Summary will update on new commits.}