feat(contract): link interface docs to code with drift check

[Saboleee]

Add check-interface-docs-drift script and npm scripts; wire into release-check. Align docs/interfaces with actual contractimpl entrypoints and fix source paths.

Made-with: Cursor

Summary

Changes

Test Plan

Automated tests added or updated

• Unit tests (backend/src/**/*.spec.ts) — service/guard/decorator logic in isolation
• Integration / e2e tests (backend/test/**/*.e2e-spec.ts) — HTTP round-trips with mocked infrastructure
• Frontend component tests (frontend/src/**/*.test.{ts,tsx}) — React component behaviour
• Frontend e2e tests (frontend/e2e/**/*.spec.ts) — Playwright browser flows
• Contract tests (contract/) — Soroban/Rust unit tests via cargo test
• No new tests required — explain why: ___

How to run the tests locally

# Backend unit tests
cd backend && npm test

# Backend e2e tests (requires no live DB — uses in-memory mocks)
cd backend && npm run test:e2e

# Frontend component tests
cd frontend && npx vitest run

# Frontend e2e tests (requires dev server on :3000 and API on :3001)
cd frontend && npx playwright test

# Contract tests
cd contract && cargo test

closes #614

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