feat: toast notifications, auth fix, accessibility & mobile improvements

[lbowsher]

Summary

• Toast system: Installed sonner and replaced all 10 alert() calls across draft-room, draft-queue, and league-home with toast.success() / toast.error() / toast.warning()
• Auth security: Replaced deprecated getSession() with getUser() in login page and auth-button-server (validates JWT server-side)
• Auth button styling: Fixed hardcoded text-gray-400 → text-muted-foreground so it respects active theme
• Reduced motion: Added prefers-reduced-motion: reduce CSS media query to disable animations for users who need it
• Mobile responsiveness: Commissioner controls now wrap on small screens; weekly score columns hidden on mobile (only total shown)
• Keyboard accessibility: Added skip-to-content link in root layout, focus-visible rings on theme toggle items and Previous Leagues button
• Loading skeleton: Replaced generic spinner on home page with card-shaped skeleton matching the team list layout

Test plan

• Trigger a toast: copy a league invite link on the league page — should show bottom-right toast instead of browser alert
• Verify login still works (getUser change)
• Check auth button text color adapts across themes (no more hardcoded gray)
• Enable "Reduce motion" in OS accessibility settings — verify no animations play
• Resize league page to mobile width — commissioner buttons should wrap, weekly scores should hide
• Tab through the app — skip-to-content link should appear on first Tab press
• Navigate to home page with slow connection / loading state — should show skeleton cards

🤖 Generated with Claude Code