Fix SonarQube issues: string duplication and cognitive complexity

[devin-ai-integration]

Summary

Fixes two High severity SonarQube issues in the github-mcp-server codebase:

1. go:S1192 - String literal duplication: Extracted ErrFailedToGetGitHubClient constant to eliminate 40+ duplicate occurrences of "failed to get GitHub client: %w"
2. go:S3776 - Cognitive complexity: Refactored ManageNotificationSubscription by extracting executeNotificationSubscriptionAction helper function to reduce complexity from 17 to ≤15

Changes

String Duplication Fix

• Added ErrFailedToGetGitHubClient constant in pkg/github/server.go
• Replaced 40+ instances across 9 files:
  • pkg/github/actions.go (14 instances)
  • pkg/github/repositories.go (12 instances)
  • pkg/github/issues.go (7 instances)
  • pkg/github/notifications.go (6 instances)
  • pkg/github/pullrequests.go (multiple instances)
  • pkg/github/search.go (3 instances)
  • pkg/github/code_scanning.go (2 instances)
  • pkg/github/secret_scanning.go (2 instances)
  • pkg/github/repository_resource.go (1 instance)

Note: pkg/github/search_utils.go was intentionally excluded as it uses a dynamic prefix pattern: fmt.Errorf("%s: failed to get GitHub client: %w", errorPrefix, err)

Cognitive Complexity Fix

• Extracted executeNotificationSubscriptionAction helper function that encapsulates the switch statement for different notification actions (ignore/watch/delete)
• Simplified ManageNotificationSubscription handler by delegating action execution to the helper
• Maintained identical functionality while reducing nesting levels

Testing

✅ All lint checks passed (./script/lint - 0 issues)
✅ All tests passed (./script/test)

Review Checklist

Please pay special attention to:

• Error formatting: Verify that fmt.Errorf(ErrFailedToGetGitHubClient, err) still produces the expected error messages with proper wrapping
• Invalid action detection: The refactored code uses if apiErr.Error() == fmt.Sprintf("invalid action: %s", action) to distinguish invalid action errors from API errors - confirm this pattern is reliable
• Response cleanup: Ensure defer func() { _ = resp.Body.Close() }() is still called correctly after the refactoring
• Cognitive complexity: Confirm the extracted helper function successfully reduces complexity while maintaining the same behavior

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Link to Devin run: https://app.devin.ai/sessions/d7851a5770a441d9a7e342cc1c5d63cd
Requested by: Shawn Azman (@ShawnAzman)

[devin-ai-integration]

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[sonarqubecloud]

Quality Gate failed

Failed conditions
21.2% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud