fix(auth): add error_tracking_read OAuth2 scope for error-tracking commands

[platinummonkey]

Summary

Adds the error_tracking_read OAuth2 scope to enable error-tracking commands when using OAuth2 authentication. Resolves authentication issues where error-tracking commands would fail with 401 Unauthorized when using OAuth2.

Changes

• pkg/auth/types/types.go:103 - Added error_tracking_read to DefaultScopes()
• pkg/auth/types/types_test.go:176 - Updated test expectations for new scope
• docs/OAUTH2.md:227 - Documented the error_tracking_read scope
• docs/TROUBLESHOOTING.md:109 - Added comprehensive OAuth2 troubleshooting section for error-tracking
• cmd/error_tracking.go:34 - Updated help text with authentication notes

Background

The error-tracking commands (pup error-tracking issues search|get) were implemented without adding the required OAuth2 scope. According to Datadog's API documentation, the error_tracking_read scope is required for Error Tracking API endpoints.

Scope Availability Note

While the error_tracking_read scope is documented and valid, there may be edge cases where Datadog's OAuth2 authorization endpoint rejects it during login (e.g., for DCR clients or certain org configurations). The PR includes comprehensive troubleshooting documentation with an API key authentication workaround.

Testing

# Run unit tests
go test ./pkg/auth/types/... -v
go test -run TestErrorTracking ./cmd/... -v

# Manual OAuth2 flow test (requires Datadog account)
pup auth logout
pup auth login  # Should succeed with new scope
pup error-tracking issues search --from=1d

All existing tests pass. The new scope is validated in TestDefaultScopes().

Related Issues

Closes #45

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🤖 Generated with Claude Code

[platinummonkey]

Note: this is blocked until this route is properly included in OAuth scopes in the backend.

[github-actions]

📊 Test Coverage Report

Overall Coverage: 81.7%

Threshold: 80% ✅

Coverage by Package

## Coverage by Package

- github.com/DataDog/pup/pkg/auth/callback/server.go:40: 81.2%
- github.com/DataDog/pup/pkg/auth/dcr/client.go:28: 100.0%
- github.com/DataDog/pup/pkg/auth/dcr/types.go:24: 100.0%
- github.com/DataDog/pup/pkg/auth/oauth/client.go:22: 100.0%
- github.com/DataDog/pup/pkg/auth/oauth/pkce.go:24: 85.7%
- github.com/DataDog/pup/pkg/auth/storage/factory.go:53: 94.7%
- github.com/DataDog/pup/pkg/auth/storage/keychain.go:44: 42.9%
- github.com/DataDog/pup/pkg/auth/storage/storage.go:58: 71.4%
- github.com/DataDog/pup/pkg/auth/types/types.go:23: 100.0%
- github.com/DataDog/pup/pkg/client/client.go:32: 94.4%
- github.com/DataDog/pup/pkg/config/alias.go:26: 100.0%
- github.com/DataDog/pup/pkg/config/config.go:22: 100.0%
- github.com/DataDog/pup/pkg/formatter/formatter.go:31: 100.0%
- github.com/DataDog/pup/pkg/useragent/useragent.go:32: 100.0%
- github.com/DataDog/pup/pkg/util/time.go:20: 95.8%

## Summary

total:								(statements)		81.7%

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📈 Coverage Status: ✅ PASSED - Coverage meets minimum threshold

_{Updated for commit 157a4e3}