Add checkout flows and empty-state CTAs

[vickydve]

Summary

• Added contextual CTA support for empty states, including interactive clear-filter and upload-first-asset actions.
• Wired the search empty state to clear active search filters from the empty result view.
• Implemented the XLM checkout modal UI showing payment amount, network fee, and total.
• Integrated Freighter signing for XLM checkout payments and capture of the submitted transaction hash.
• Added the fiat credit-card checkout screen shell with order summary and secure payment form layout.

Testing

• pnpm --filter web lint
• pnpm --filter web exec tsc --noEmit currently fails due to pre-existing unrelated TypeScript issues in tests/imports:
  • missing @/services/mockRequests
  • missing ../spv-step
  • missing @/store/verificationStore
  • outdated GasFeeEstimator test props/exports
  • invalid screen.getByAlt usage

Closes #395
Closes #404
Closes #405
Closes #406

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[Tybravo]

@vickydve
Good work done and than you for contributing