test: add useDebounce integration tests and state management docs (#489 #490 #496)

[Chidimj]

Summary

• Add integration test for useDebounce hook not updating value before delay elapses #496 - Integration test for useDebounce hook: asserts debounced value stays unchanged during the delay window and updates after timer advances past it (fake timers, deterministic)
• Add integration test for debounced search input only triggering one API call after rapid typing #489 - Integration test for debounced creator search: asserts API is called exactly once after rapid typing burst and uses the final input value, with no calls fired mid-burst
• Add docs for client state management approach and when to use local vs server state #490 - Docs for client state management: documents the server-state (React Query) vs ephemeral UI state (useState) rule, query invalidation vs manual refetch guidance, and an anti-pattern example

Test plan

• pnpm test src/hooks/tests/useDebounce.test.tsx -- 3 tests pass
• pnpm test src/pages/tests/LandingPage.debouncedSearch.integration.test.tsx -- 3 tests pass
• docs/state-management.md reviewed for accuracy against codebase patterns

Closes #489
Closes #490
Closes #496

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[github-actions]

👋 Hey @Chidimj, thanks for your contribution!

This PR is targeting main directly. We use main for stable releases only — all contributions should be opened against the dev branch instead.

Please close this PR and reopen it with dev as the base branch. If you're unsure how to do that, you can change the base branch using the Edit button at the top of this PR page.

Closing this PR automatically. See you in dev! 🚀