Update frontend dependencies and resolve npm advisories

[ProfessorPolymorphic]

Summary

Consolidates and supersedes the five stale Dependabot pull requests: #187, #188, #189, #190, and #191.

• updates react-router-dom to 7.18.1
• updates Tailwind CSS and its Vite plugin to 4.3.3
• updates @types/node within the existing major to 25.9.5
• updates Vite to 8.1.5
• updates typescript-eslint to 8.65.0
• refreshes transitive dependencies to resolve npm security advisories

Validation

• 41 frontend tests pass
• ESLint passes
• production build passes
• npm audit --audit-level=low reports 0 vulnerabilities