Fix homepage showcase layout shift

[decofe]

Summary

• reserve a stable visual/code panel height on the homepage transaction and token showcases
• prevent section height changes when toggling between Diagram and Code

Verification

• pnpm check:types
• pnpm build (completed; transient GitHub fetch timeout logged during changelog SSG, build exited 0)
• pnpm exec biome check src/marketing/app/_components/TransactionsShowcase.tsx src/marketing/app/_components/TokensShowcase.tsx
• Playwright measurements on http://localhost:5173/ confirmed both affected sections keep identical bounding-box heights across Diagram -> Code -> Diagram

Prompted by: @tmm

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Project	Deployment	Actions	Updated (UTC)
tempo-docs	Ready	Preview, Comment	Jun 24, 2026 12:39am