fix: consolidate pool service

[Meet-hybrid]

• ## Summary

• Removed the redundant pool.service.ts.
• Updated SponsorOnboarding.tsx to use sponsorsService.getPoolInfo().
• Confirmed all pool consumers use the shared sponsors service.
• Fixed an existing lint issue in vouching.service.ts.

Testing

• npm run lint ✅
• TypeScript check ✅
• tsc -b ✅
• git diff --check ✅
• npm run build ⚠️ Environment Bus error
• npm test ⚠️ Environment Bus error

Closes #57

[EmeditWeb]

Review verdict: ✅ APPROVE

Verified locally on this branch: build, lint, and test all pass (21 tests). The consolidation is correct — SponsorOnboarding now calls sponsorsService.getPoolInfo() (which exists and is identical to the removed poolService.getPoolInfo()), and the redundant src/services/pool.service.ts is deleted with no other references left.

Two notes:

1. The change to src/services/vouching.service.ts (_txHash → _) is unrelated to consolidating the pool service — but it's harmless and, usefully, it fixes the pre-existing lint error on main that is currently making every Web PR's CI red. Because of that, merging this PR first would un-red the other Web PRs' CI.
2. The PR's own CI shows red, but that appears stale — a fresh run should pass. Please re-trigger CI.

Approve.