chore: Add security header (#10694)

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---

## PR-Codex overview
This PR adds a Content-Security-Policy header with frame-ancestors
'self' value to improve security in `next.config.mjs`.

### Detailed summary
- Added Content-Security-Policy header with frame-ancestors 'self'
value.

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question}`

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apps/gamification/next.config.mjs

@@ -75,6 +75,10 @@ const nextConfig = {
             key: 'Cross-Origin-Opener-Policy',
             value: 'same-origin-allow-popups',
           },
+          {
+            key: 'Content-Security-Policy',
+            value: `frame-ancestors 'self'`,
+          },
         ],
       },
     ]