Implement global search

[0bkevin]

Closes #3

Summary

• add a global search component for authenticated app pages
• search app pages, items, and admin users when permitted
• lazy-load searchable item/user data when the search field is focused

Verification

• npm run build
• ./node_modules/.bin/biome check --apply-unsafe --files-ignore-unknown=true src/components/Common/GlobalSearch.tsx src/components/Common/Navbar.tsx src/routes/_layout.tsx