feat: design template detail

[lyon-1050]

Here's a summary of what was implemented:

Files created/modified:

apps/frontend/src/components/app/templates/TemplateDetailView.tsx
- Header — template name (h1), category badge, "Stellar" label
- OverviewSection — preview image with emoji fallback on missing
URL or load error
- FeatureListSection — all features with enabled/disabled
indicators; hidden when empty
- StellarConfigSection — network options, Horizon URL
required/optional, Soroban RPC required/optional; hidden when
schema absent
- MetadataSection — version, total deployments, last updated;
hidden when metadata not provided
- CTASection — "Customize & Deploy" button that calls
onCustomize

• apps/frontend/src/app/app/templates/[id]/page.tsx — Next.js page
  that fetches template + metadata in parallel, shows
  LoadingSkeleton / ErrorState / TemplateDetailView, and breadcrumbs
  Home → Templates →
• apps/frontend/src/components/app/templates/index.ts — added
  TemplateDetailView export

apps/frontend/src/components/app/templates/TemplateDetailView.test
.tsx — 17 tests covering all sections, edge cases (empty features,
missing stellar config, missing metadata, image fallback, CTA
click)

Edge cases handled:

• previewImageUrl empty or image load failure → emoji fallback
• features: [] → feature section not rendered
• customizationSchema.stellar absent → Stellar section not
• metadata not provided → metadata section not rendered
• metadata.lastUpdated as string or Date (defensive coercion)

closes #14

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