fix: add type safety, a11y, responsive grids in Dashboard

fix: add error handling, type safety, a11y in auth page

fix: remove dead code, add accessibility attrs in page.tsx

Fix: Supabase client type safety - return null instead of unsafe cast

Fix: Add mobile viewport settings and Viewport type import

Recreate auth page with fixed emoji encoding

Delete app/auth/page.tsx

Recreate page.tsx with fixed emoji encoding

Delete app/page.tsx

Fix emoji encoding and remove duplicate content in page.tsx

Fix emoji encoding - replace double-encoded UTF-8 with correct Unicode

Fix typo in button text condition

Add client directive to CodeReviewer component

Add 'use client' directive to SpecEngine component

Add client directive to SecurityScanner component