Fix sidebar active state after navigation

[vicksiyi]

Summary

• Sync sidebar active menu state whenever the route pathname changes.
• Keep Chatflows selected when navigating back through the Flowise logo/default route.

Fixes #6510

Tests

• git diff --check
• pnpm --dir packages/ui build

[gemini-code-assist]

Code Review

This pull request refactors the NavItem component to use the useLocation hook from react-router-dom instead of accessing document.location.pathname directly, and adds location.pathname to the useEffect dependency array to ensure the active menu item updates correctly on route changes. The reviewer suggested optimizing this hook by checking if the menu item is already open before dispatching MENU_OPEN to prevent redundant Redux dispatches and unnecessary re-renders, as well as caching the split pathname.

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