docs: update custom error page

[halvaradop]

☕️ Reasoning

The PR updates the Custom Error page by re-exporting the SignInPageErrorParam and ErrorPageParam types from the next-auth package.
This allows creating an object map of all possible errors that may occur during the authentication workflow.

🧢 Checklist

• Documentation
• Tests
• Ready to be merged

🎫 Affected issues

📌 Resources

• Security guidelines
• Contributing guidelines
• Code of conduct
• Contributing to Open Source

[vercel]

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Project	Deployment	Preview	Comments	Updated (UTC)
auth-docs	Ready	Preview	Comment	Aug 29, 2025 8:51pm

1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
next-auth-docs	Ignored	Preview		Aug 29, 2025 8:51pm

[vercel]

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[codecov]

Codecov Report

❌ Patch coverage is 7.40741% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 36.81%. Comparing base (39dd3b9) to head (9da84a3).

Files with missing lines	Patch %	Lines
packages/core/src/types.ts	0.00%	25 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13200      +/-   ##
==========================================
- Coverage   38.76%   36.81%   -1.95%     
==========================================
  Files         200      197       -3     
  Lines       32323    31352     -971     
  Branches     1393     1249     -144     
==========================================
- Hits        12529    11543     -986     
- Misses      19794    19809      +15     

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