feat(sprint-5): Phase 3 — Wire dashboard + members to React Query

- Dashboard: useClubStatsQuery + useRecentDistributionsQuery with fallback
- Members list: useMembersQuery with debounced search + pagination
- Member detail: useMemberQuery + useUpdateMemberMutation
- Add member: useCreateMemberMutation with invalidation
- All pages show loading skeletons during fetch
- Graceful fallback to mock data when backend unavailable
- New useDebounce hook for search input (300ms delay)

cannamanage-frontend/src/hooks/use-debounce.ts

@@ -0,0 +1,16 @@
+import { useEffect, useState } from "react"
+
+/**
+ * Debounce a value by a given delay.
+ * Returns the debounced value that only updates after the delay.
+ */
+export function useDebounce<T>(value: T, delay: number): T {
+  const [debouncedValue, setDebouncedValue] = useState<T>(value)
+
+  useEffect(() => {
+    const timer = setTimeout(() => setDebouncedValue(value), delay)
+    return () => clearTimeout(timer)
+  }, [value, delay])
+
+  return debouncedValue
+}