fix(coinbase): modernize OAuth integration

[nijel]

Coinbase's legacy OAuth contract and unversioned user requests can cause otherwise valid logins to fail with 403 responses. Adopt the current endpoints, scopes, version header, and revocation parameters, and treat provider 403s as authentication failures.

Closes #1036

[codecov]

Codecov Report

❌ Patch coverage is 96.96970% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.29%. Comparing base (d56fe6d) to head (fa51579).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
social_core/backends/coinbase.py	87.50%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1901      +/-   ##
==========================================
+ Coverage   87.17%   87.29%   +0.11%     
==========================================
  Files         352      352              
  Lines       13624    13696      +72     
  Branches      671      674       +3     
==========================================
+ Hits        11877    11956      +79     
+ Misses       1504     1495       -9     
- Partials      243      245       +2     

Flag	Coverage Δ
unittests	87.29% <96.96%> (+0.11%)	⬆️

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve email access in the default scope

For Coinbase applications that rely on the backend's default scopes, wallet:user:read does not grant access to the separately protected email field, so get_user_details() now returns email="" where the legacy user scope returned the user's email. This breaks email-required pipelines and can prevent email-based association for otherwise valid logins; include wallet:user:email in the defaults to preserve the backend's existing behavior.

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