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>

package.json

@@ -22,7 +22,6 @@
     "@kinescope/react-kinescope-player": "^0.5.4",
     "@prisma/adapter-pg": "^7.6.0",
     "@prisma/client": "^7.6.0",
-    "@tailwindcss/typography": "^0.5.19",
     "@tiptap/extension-image": "^3.22.2",
     "@tiptap/extension-link": "^3.22.2",
     "@tiptap/extension-placeholder": "^3.22.2",
@@ -44,10 +43,8 @@
     "react-dom": "19.2.4",
     "remark-parse": "^11.0.0",
     "resend": "^6.10.0",
-    "shadcn": "^4.1.2",
     "sonner": "^2.0.7",
     "tailwind-merge": "^3.5.0",
-    "tw-animate-css": "^1.4.0",
     "unified": "^11.0.5",
     "zod": "^4.3.6"
   },