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>

src/app/api/admin/lesson-files/route.ts

@@ -22,6 +22,9 @@ export async function POST(req: NextRequest) {
   const label = (form.get("label") as string | null)?.trim() || null;
   if (!file || !lessonId) return NextResponse.json({ error: "Missing fields" }, { status: 400 });
 
+  const MAX_BYTES = 50 * 1024 * 1024;
+  if (file.size > MAX_BYTES) return NextResponse.json({ error: "Файл слишком большой" }, { status: 413 });
+
   const name = label ?? file.name;
   const existing = await prisma.lessonFile.findFirst({ where: { lessonId, name } });