fix: align accent colors to indigo, remove dead Button stub, lazy-load soroban, add remittance e2e

[Ojukwu-Chinedu]

Summary

• Swap Button primary variant and focus rings from hardcoded blue-600/blue-500 to indigo-600 and the --focus-ring CSS token, matching the app's brand accent across 38+ files
• Update --focus-ring token from #2563eb (blue-600) to #4f46e5 (indigo-600) so all ring-color consumers stay consistent
• Delete unused global_ui/Button.tsx stub and its test — no imports reference it; the real component is ui/Button.tsx
• Dynamic-import @stellar/stellar-sdk on the repay route so the full SDK bundle is excluded from the initial chunk
• Add Playwright e2e spec for the send-remittance flow covering wallet-not-connected guard, validation errors, and the happy-path submit + redirect

Files changed

• frontend/src/app/components/ui/Button.tsx — indigo accent + tokenised focus ring
• frontend/src/app/components/ui/Input.tsx — tokenised focus ring
• frontend/src/app/[locale]/globals.css — --focus-ring updated to indigo-600
• frontend/src/app/components/global_ui/Button.tsx — deleted
• frontend/src/app/components/global_ui/Button.test.tsx — deleted
• frontend/src/app/[locale]/repay/[loanId]/page.tsx — dynamic import of soroban utils
• frontend/e2e/send-remittance.spec.ts — new e2e spec

Testing

• Existing unit tests pass (Jest)
• E2e spec covers negative and positive paths for send-remittance
• No remaining ring-blue-500 in Button/Input components

Fixes

closes #1243
closes #1244
closes #1247
closes #1249