feat: adding localstorage hook

[nieblara]

Description

What does this PR do?

Introduces a useLocalStorage hook to provide a useState-like API for persistent localStorage storage, replacing manual localStorage read/write patterns across multiple providers.

Changes:

• New useLocalStorage hook with:

  • Type-safe generics
  • SSR safety (typeof window checks)
  • Optional cross-tab synchronization via StorageEvent
  • Custom serializers/deserializers for non-JSON values
  • Smart persistence (doesn't write defaults until explicitly set)
  • Returns [value, setValue, remove] tuple

• Refactored providers to use the hook:

  • useToolbarVisibility - Reduced from 77 lines to ~30 lines, removed duplicate cross-tab sync logic
  • StarredFlagsProvider - Now uses hook instead of loadStarredFlags/saveStarredFlags

• Cleanup:

  • Used refs for serializers to prevent unnecessary effect re-runs when inline functions are passed

Backward Compatibility

Data formats in localStorage are identical to the previous implementation:

Key	Format
ld-toolbar-starred-flags	JSON array ["flag1", "flag2"]
ld-toolbar-environment	Raw string staging
ld-toolbar-project	Raw string my-project
ld-toolbar-disabled	String "true" or item removed

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation (changes to documentation only)
• 🔧 Refactor (code change that neither fixes a bug nor adds a feature)
• 🎨 Style (formatting, missing semicolons, etc; no production code change)
• ⚡ Performance (code change that improves performance)
• ✅ Test (adding missing tests, refactoring tests; no production code change)
• 🔨 Chore (updating grunt tasks, build process, etc; no production code change)

[cspath1]

Thanks for helping clean this up!