chore: remove dead code, unused CSS, unused components, and clean up git tracking

- Remove storage/logs/ and prod.log from git tracking; add to .gitignore
- Remove unused AvatarCarousel and ArticleSlider components
- Remove unused SkeletonTable export from ui.tsx
- Remove unused ChevronDown import from admin layout
- Remove 13 unused CSS classes (icon-base, nav-*, navigation-icon*, .app.dark,
  text-body, transition-base, card-base, admin-info-grid, .coin.*)
- Remove duplicate translation keys (openMenu/closeMenu in en.json)
- Fix admin-bans to use Prisma-generated bans_type enum
- Create shared AdminPageHeader component and formatDate utility
- Add logger and generateRequestId for structured logging
- All 58 tests pass, typecheck clean, build succeeds

.gitignore

@@ -6,3 +6,7 @@ next-env.d.ts
 *.tsbuildinfo
 # Prisma client is generated by `prisma generate`
 src/generated/
+# Runtime logs (not part of the codebase)
+storage/logs/
+prod.log
+*.log