feat: add Zustand stores and custom hooks

frontend-mobile/store/searchStore.ts

@@ -0,0 +1,27 @@
+import { create } from 'zustand';
+import { Medicine } from '../types';
+
+interface SearchState {
+  query: string;
+  results: Medicine[];
+  isLoading: boolean;
+  error: string | null;
+  setQuery: (query: string) => void;
+  setResults: (results: Medicine[]) => void;
+  setLoading: (loading: boolean) => void;
+  setError: (error: string | null) => void;
+  clearResults: () => void;
+}
+
+export const useSearchStore = create<SearchState>((set) => ({
+  query: '',
+  results: [],
+  isLoading: false,
+  error: null,
+
+  setQuery: (query) => set({ query }),
+  setResults: (results) => set({ results, isLoading: false }),
+  setLoading: (isLoading) => set({ isLoading }),
+  setError: (error) => set({ error, isLoading: false }),
+  clearResults: () => set({ results: [], query: '', error: null }),
+}));