feat: build per-token volume chart

[newmattock]

Fixes #66

Summary

• add a contract-backed per-token volume chart to the protocol analytics page
• parse get_contract_stats() weekly or flat per-token volume fields into 30/90 day stacked Recharts data
• add USD-equivalent summary totals for USDC, EURC, and XLM using oracle prices when present
• add transformation tests and fix the Vitest @ alias to match tsconfig

Validation

• npm test -- src/utils/tests/perTokenVolume.test.ts --reporter verbose
• npx eslint app/analytics/page.tsx src/components/charts/PerTokenVolumeChart.tsx src/utils/perTokenVolume.ts src/utils/tests/perTokenVolume.test.ts vitest.config.ts
• npm run build
• git diff --check
• local smoke: GET /analytics returned HTTP 200 on port 3014

Note: full-file lint for src/utils/soroban.ts still reports pre-existing no-explicit-any errors below this change.

[newmattock]

Closing this older duplicate in favor of the newer clean branch in #120 for the same issue (#66). Keeping one active PR should make review easier.