feat: optimize context, add auth middleware, consolidate components, add query keys

[Leothosine]

Summary

This PR addresses four issues across performance, security, structure, and caching:

• Context API Optimization: Added useMemo to the ToastContext provider value so the context object is only recreated when its contents actually change, preventing unnecessary re-renders in all consumers
• Route Handler Authentication: Added
  equireAuth middleware helper in src/lib/authMiddleware.ts - a single function that validates the Authorization: Bearer header and returns a 401 response if missing or invalid, ready to be used across all protected API routes
• Duplicate Component Definitions: Added src/components/index.ts as the canonical barrel export for all shared UI components, establishing @/components as the single source of truth and providing a migration path away from @/app/components
• Query Key Factory: Added src/lib/queryKeys.ts with a structured key factory covering courses, user, search, bookmarks, and notes - ensures consistent, type-safe cache keys across all data-fetching hooks

Changes

• src/context/ToastContext.tsx - memoized context value with useMemo
• src/lib/authMiddleware.ts -
  equireAuth helper for route protection
• src/components/index.ts - canonical component barrel export
• src/lib/queryKeys.ts - query key factory for all API resources

closes #162
closes #163
closes #171
closes #174

[drips-wave]

@Leothosine Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits