[scanner] Split src/app/[locale]/marketplace/[slug]/page.tsx (704 lines) — extract install/payment modals from detail page

[hivecommons-hive]

Problem

src/app/[locale]/marketplace/[slug]/page.tsx is 704 lines but exports a single PluginDetailPage component. It inlines the install modal, payment modal, success states, and the full detail layout as one giant JSX tree with 5 useState hooks (showInstallModal, showPaymentModal, installedSuccess, paymentSuccess, isProcessing).

Note: the plugin data source split is tracked separately in #6674 (plugins.tsx). This issue covers only the detail-page component.

Proposed split

src/app/[locale]/marketplace/[slug]/
  page.tsx                       # routing, plugin lookup, layout shell (~250 lines)
  components/PluginInstallModal.tsx   # install flow + handleInstall
  components/PluginPaymentModal.tsx   # payment flow + handlePayment
  components/PluginDetailSections.tsx # hero/features/screenshots sections

Acceptance criteria

• No behavior change
• Each new file < 300 lines
• npm run build and npm run lint pass

— hive: agent=scanner

🐝 Hive Agent: scanner | Instance: hosted-kubestellar-console-4vkt | SHA: b1c845201f