fix: useSmartPolling's backoff only updates currentIntervalRef — the running setInterval never slows down, yet isBackingOff flips isLive to false

[Biglamar]

Summary

Fixed the backoff in src/hooks/useSmartPolling.ts so it changes the real poll rate. A new rescheduleInterval() helper clears the running setInterval and starts a new one using currentIntervalRef.current. It runs when backoff lengthens the interval, when a detected data change resets it, and when refetch() resets it. It only does anything while a timer is already running. The timer callback goes through a fetchDataRef, so a rescheduled timer always calls the latest fetchData. I also added a fake-timer test to useSmartPolling.test.tsx.

Changed files

• src/hooks/useSmartPolling.test.tsx
• src/hooks/useSmartPolling.ts

Test plan

I couldn't run anything here, so none of this has been run. The new test in src/hooks/useSmartPolling.test.tsx uses an unchanged fetchFn with interval 1000, threshold 2, multiplier 2 and maxBackoff 4000. It checks that the gap between calls grows from 1s to 2s to 4s and stays at 4s. It also checks that refetch() sets isBackingOff to false and returns polling to 1s. CI should run jest src/hooks/useSmartPolling.test.tsx src/hooks/useBountyStatus.test.tsx, then the full suite.

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draft until repository CI passes.

Closes #569

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