Add real-time staff polls

[owenqwenstarsky]

Summary

• add staff-only poll creation with durable, changeable votes and compact accessible results
• replace five-second polling with replica-safe PostgreSQL LISTEN/NOTIFY and authorized SSE refresh signals
• add dedicated vote/stream rate limits, live hidden-poll staff verification, reconnect reconciliation, and slow fallback polling
• update poll creation, thread badges, component/route/integration tests, and the two-viewer browser journey

Verification

• npm test — 650 tests passed
• npm run test:coverage — coverage thresholds passed
• npm run lint
• npm run typecheck
• npm run build
• PostgreSQL poll notification integration passed for insert, update, and delete
• poll feature E2E passed, including two-second cross-viewer updates, vote changes, reconnect recovery, and mobile layout

Closes #19