SearchFilter: debounce input to fix typing flicker (#274)

[ptrlrd]

Closes #274.

Root cause

Every keystroke in the cards/relics/potions/etc. search box triggered:

1. setSearch (state update)
2. router.replace (URL update)
3. useEffect deps include search → API fetch
4. New cards arrive → another re-render

That cascade produced the visible flicker while typing.

Fix

Decoupled the <input> value from the upstream search prop. A local draft state advances on every keystroke (instant feedback), and the consumer's onSearchChange only fires 200ms after typing stabilizes. External search prop changes (URL → state sync, clear-filter buttons) still flow back into the draft.

Implemented inside SearchFilter.tsx so all 9 consumers (cards, relics, potions, powers, events, encounters, enchantments, guides, browse) inherit the fix without touching their wiring.

Uses a ref to hold the latest onSearchChange callback so the debounce timer isn't reset by parent re-renders that produce fresh inline arrow functions.