improve: Add hint about making GitHub org membership public in error messages (#772)

When users try to publish to a GitHub organization but don't have
permission, the error message now includes a helpful hint suggesting
they may need to make their organization membership public in GitHub
settings.

This addresses the issue where users couldn't understand why they were
unable to publish servers from organization repositories, even when they
were members of the organization.

Fixes #398

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---------

Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: adam jones <domdomegg@users.noreply.github.com>

internal/api/handlers/v0/publish.go

@@ -84,5 +84,10 @@ func buildPermissionErrorMessage(attemptedResource string, permissions []auth.Pe
 	}
 	errorMsg += ". Attempting to publish: " + attemptedResource
 
+	// Add helpful hint for GitHub organization publishing issues
+	if strings.HasPrefix(attemptedResource, "io.github.") {
+		errorMsg += ". If you're trying to publish to a GitHub organization, you may need to make your organization membership public in your GitHub settings: https://docs.github.com/en/account-and-profile/how-tos/organization-membership/publicizing-or-hiding-organization-membership"
+	}
+
 	return errorMsg
 }