backend: mount v1 pool notification event routes

[artylobos]

Closes #872

Summary

• mount the existing pool, notifications, and events routers under /api/v1 while leaving the legacy /api/* routes in place
• add integration coverage for /api/v1/pool/stats, /api/v1/notifications, and /api/v1/events/status with valid auth/API-key headers
• format the existing two frontend e2e specs that currently fail the repository-wide frontend Prettier check
• fix the newly merged service-worker manifest typing so the frontend build can type-check on the updated main branch

Validation

• npm test -- --runTestsByPath src/__tests__/apiV1Mounts.test.ts --runInBand
• npm test -- --runInBand -> 213 passed, 18 skipped
• npm run build
• npm run typecheck
• npm run lint -> exit 0 with existing repository warnings
• npx prettier --check src/app.ts src/__tests__/apiV1Mounts.test.ts
• npx --yes prettier@3.8.1 --check frontend/e2e/borrower-repay-flow.spec.ts frontend/e2e/lender-withdraw-flow.spec.ts
• npx prettier --check . from frontend
• npx tsc --noEmit --pretty false from frontend
• git diff --check

Note: local npm run build in frontend stops before application type-check on macOS because @parcel/watcher-darwin-x64 is missing from the optional native install; GitHub Linux CI reaches the Next.js type-check and is the full frontend build verifier.

No secrets, wallet keys, deployment values, or private/system context included.