feat: build per-token volume chart

[newmattock]

Fixes #66

Summary

• Add get_contract_stats() loading to the public analytics page.
• Add a PerTokenVolumeChart with 30/90 day range controls, USDC/EURC/XLM stacked bars, and a USD-equivalent summary row.
• Add a tolerant per-token volume parser for weekly contract stats, all-time per-token totals, and invoice-derived fallback data.
• Add focused data transformation tests.
• Carry narrow current-main build fixes needed for validation.

Validation

• npm test -- src/utils/__tests__/per-token-volume.test.ts --pool forks --maxWorkers 1 --reporter verbose
• npm run lint -- src/utils/per-token-volume.ts src/utils/__tests__/per-token-volume.test.ts src/components/charts/PerTokenVolumeChart.tsx app/analytics/page.tsx src/utils/soroban.ts app/governance/page.tsx src/components/TokenSelector.tsx src/utils/federation.ts
• git diff --check
• npm run build
• curl -I http://127.0.0.1:3035/analytics