chore: enforce exhaustive React hook dependencies (#4712)

## Summary

Enables exhaustive React Hook dependency checking and resolves the
existing violations across the dashboard and React hooks package.
Effects and callbacks now track current values without introducing
request, subscription, or render loops.

## Design

Dependencies are included directly when the hook lifecycle should follow
them. Timers, Remix fetchers, and realtime subscriptions use stable
callbacks or latest-value refs where restarting work would change
behavior.

Unnecessary memoization was removed where ordinary derivation is
clearer. Full lint and typechecks for the webapp and React hooks package
pass.