fix(docs): add noopener to verify redirect example

[maho0638]

Summary

Adds noopener,noreferrer to the window.open(..., '_blank') example in the Base Verify redirect flow.

Why

The current example opens a new browsing context without explicitly preventing opener access. Adding noopener,noreferrer makes the copied example safer for production use.

Fixes #1470.

Test plan

• Verified this PR only updates docs/base-account/guides/verify-social-accounts.mdx
• Confirmed the code example still opens the Base Verify deep link in a new tab/window

[cb-heimdall]

🟡 Heimdall Review Status

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