Add visibility-aware Team Manager refresh

[itsreverence]

Summary

• refresh Team Manager data every 60 seconds only while the Team Manager is visible
• refresh when the application regains focus, with a short duplicate-request throttle
• add a compact manual refresh control and checked/updated/error status
• preserve the last successful roster, lineup, waiver, matchup, activity, and AI context when a background refresh fails
• ignore regenerated timestamps when deciding whether Sleeper data meaningfully changed
• prevent stale concurrent requests from overwriting newer Team Manager state

Validation

• npm ci
• npm run check
• npm test (111 passed, 2 platform-specific tests skipped)
• npm run build
• npm audit --omit=dev --audit-level=high (0 production vulnerabilities)
• git diff --check
• Impeccable detector on changed UI targets (0 findings)
• live Sleeper league smoke: initial load, manual refresh, no-change completion, and 60-second automatic refresh
• confirmed roster remains visible throughout background refreshes