fix: prevent React 418 hydration mismatch on compare tools and client-only components

[tiberiuichim]

Description

Fixes React error #418 (hydration mismatch) when navigating or opening tool pages while tools are saved in comparison storage (localStorage).

Changes

1. Hydration safety for useCompareTools and CompareToolsPanel:
   • Added useHasMounted hook to safely defer client-only state derived from browser localStorage until after the component has mounted.
   • During SSR and the initial client hydration pass, selected tools evaluate to empty ([]), ensuring isSelected and isLimitReached match the server-rendered HTML.
   • Guarded <CompareToolsPanel /> with if (!hasMounted || effectiveSelectedTools.length === 0) return null; so that the floating panel is not rendered during initial hydration when SSR returned null.
2. Hydration safety for withClientOnly HOC:
   • Replaced __SERVER__ ? null : <WrappedComponent /> check with a post-mount lifecycle guard (useState(false) + useEffect), preventing server/client tree mismatches during initial client hydration.
3. Tests:
   • Added unit tests for useHasMounted and hasMounted in utils.test.jsx.
   • Added unit test for withClientOnly in withClientOnly.test.jsx.