feat: setup Zustand state management for wallet, pools, donations, an…

[whiteghost0001]

i Installed Zustand 4.5.5 and created four stores in frontend/src/store/:

• walletStore — wallet connection, public key, and balances (persisted to localStorage)
• poolsStore — pool list with search/filter/category state and a filteredPools() selector
• donationsStore — donation history and active donation tracking (persisted to localStorage)
• uiStore — modal open/close and sidebar toggle

closes #385

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