Apply tech debt fixes: middleware rename, React.cache, file size limits, remove dead deps

- Rename proxy.ts → middleware.ts, export proxy() → middleware() so Next.js edge
  protection actually activates (F001)
- Add PUBLIC_ROUTES entries for /forgot-password and /reset-password
- Wrap getSettings() in React.cache() to eliminate duplicate DB call in root layout (F003)
- Remove 4 console.log calls from saveLesson Server Action, keep console.error (F005)
- Add 50 MB file size guard to all 6 upload routes before arrayBuffer() read (F004)
- Remove unused deps: @tailwindcss/typography, shadcn, tw-animate-css (F008)
- Update CLAUDE.md: Prisma version 6.x → 7.x
- Add TECH_DEBT_AUDIT.md with 14 findings across 9 dimensions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -11,7 +11,7 @@
 | TypeScript | 5.x | Язык |
 | React | 19 | UI |
 | PostgreSQL | 16 | База данных |
-| Prisma | 6.x | ORM + миграции |
+| Prisma | 7.x | ORM + миграции |
 | Better Auth | latest | Аутентификация и сессии |
 | Tailwind CSS | 4.x (CSS-based config) | Стили (нет tailwind.config.ts) |
 | shadcn/ui | latest | UI-компоненты |