XSS: dangerouslySetInnerHTML renders unsanitized problem statements in 5 locations

[amaydixit11]

Issue

After reviewing the code, `dangerouslySetInnerHTML` is used in 5 locations to render problem descriptions that could come from Codeforces API, admin input, or other external sources.

Affected Files

File	Line	What's Rendered
`src/pages/potd.tsx`	258	`formatDescription(truncatedDesc)`
`src/pages/questions/[id].tsx`	447-449	`formatDescription(ques.description)`
`src/pages/questions/[id].tsx`	458-460	`formatDescription(ques.input_format)`
`src/pages/questions/[id].tsx`	469-471	`formatDescription(ques.output_format)`
`src/components/ProblemOfTheDay.jsx`	8	`formatDescription(problem.description)`

Attack Vector

If any problem description contains HTML with event handlers or script tags (from Codeforces API, or an admin accidentally pasting HTML), it will execute in the browser:

```html

```

Fix

Install DOMPurify:
```bash
npm install dompurify @types/dompurify
```

Then sanitize before rendering:
```tsx
import DOMPurify from 'dompurify';

// Replace each:

// With:

\`\`\`

[github-actions]

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