Reduce cyclomatic complexity across repository functions

[Copilot]

Refactored 8 high-complexity functions (complexity 8-21) into focused helper functions with single responsibilities. Maximum production code complexity reduced from 21 to 8.

Changes

Repository fetching functions

• getGithubRepositories (21→3): Extracted getGithubUserRepositories, shouldSkipGithubRepo, buildGithubRepository
• getGitlabRepositories (17→2): Extracted buildGitlabListOptions, getGitlabVisibility, fetchGitlabProjects, buildGitlabRepository
• getBitbucketRepositories (13→3): Extracted fetchBitbucketRepositoriesFromWorkspaces, fetchBitbucketWorkspaceRepositories, buildBitbucketRepository

Migration functions

• handleGithubCreateUserMigration (11→2): Extracted createUserMigration, processOrganizationMigrations, createOrganizationMigration
• downloadGithubUserMigrationData (10→2): Extracted pollUserMigrationStatus
• downloadGithubOrgMigrationData (9→2): Extracted pollOrgMigrationStatus
• Added defaultMigrationPollingInterval constant to replace magic number

Utility functions

• getUsername (8→5): Converted to switch statement, extracted getGithubUsername, getGitlabUsername, getBitbucketUsername
• cloneNewRepo (8→3): Extracted shouldSkipPrivateRepo, buildAuthenticatedCloneURL, buildGitCloneCommand

Example

Before:

func getGithubRepositories(client interface{}, ...) ([]*Repository, error) {
    // 50+ lines with nested loops, conditionals, and multiple responsibilities
    for {
        repos, resp, err := client.Repositories.List(...)
        for _, repo := range repos {
            if *repo.Fork && ignoreFork { continue }
            if len(githubNamespaceWhitelist) > 0 && !contains(...) { continue }
            var httpsCloneURL, sshCloneURL string
            if repo.CloneURL != nil { httpsCloneURL = *repo.CloneURL }
            // ... more inline logic
        }
    }
}

After:

func getGithubRepositories(client interface{}, ...) ([]*Repository, error) {
    if githubRepoType == "starred" {
        return getGithubStarredRepositories(ctx, client, ignoreFork)
    }
    return getGithubUserRepositories(ctx, client, githubRepoType, githubNamespaceWhitelist, ignoreFork)
}

func shouldSkipGithubRepo(repo *github.Repository, namespaceWhitelist []string, ignoreFork bool) bool {
    if *repo.Fork && ignoreFork { return true }
    namespace := strings.Split(*repo.FullName, "/")[0]
    return len(namespaceWhitelist) > 0 && !contains(namespaceWhitelist, namespace)
}

func buildGithubRepository(repo *github.Repository) *Repository {
    // Single responsibility: convert GitHub API type to internal type
}

All existing tests pass without modification. No API changes.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Improve code quality</issue_title>
<issue_description>Any PRs to improve code quality is welcome.

Some metrics/analysis to guide starting points:

# https://github.com/fzipp/gocyclo

$ ~/go/bin/gocyclo .
21 main getGithubRepositories github.go:11:1
17 main getGitlabRepositories gitlab.go:10:1
17 main newClient client.go:74:1
13 main getBitbucketRepositories bitbucket.go:10:1
11 main handleGithubCreateUserMigration github_create_user_migration.go:9:1
11 main backUp backup.go:22:1
10 main downloadGithubUserMigrationData user_data.go:93:1
9 main downloadGithubOrgMigrationData user_data.go:144:1
9 main TestCliUsage cli_test.go:15:1
8 main getUsername helpers.go:12:1
8 main handleGitRepositoryClone git_repository_clone.go:9:1
7 main getGithubOrgRepositories user_data.go:271:1
6 main createGithubUserMigration user_data.go:40:1
6 main TestGetStarredGitLabRepositories repositories_test.go:191:1
6 main main main.go:26:1
6 main setupBackupDir backup.go:75:1
5 main TestGetGithubOrganizationRepositories user_org_migration_test.go:87:1
5 main handleGithubListUserMigrations github_list_user_migrations.go:11:1
5 main TestHelperRemoteUpdateProcess backup_test.go:128:1
4 main TestGetUserOwnedOrganizations user_org_migration_test.go:39:1
4 main TestCreateGitHubUserMigrationFailOnceThenSucceed user_migration_test.go:62:1
4 main getGithubUserOwnedOrgs user_data.go:254:1
4 main TestGetBitbucketRepositories repositories_test.go:221:1
4 main TestGetGitLabPrivateRepositories repositories_test.go:165:1
4 main TestGetGitLabRepositories repositories_test.go:144:1
4 main getRepositories repositories.go:33:1
4 main initConfig options.go:9:1
4 main TestNewClient client_test.go:12:1
4 main TestSetupBackupDir backup_test.go:140:1
4 main TestHelperCloneProcess backup_test.go:116:1
4 main TestHelperPullProcess backup_test.go:104:1
3 main TestDownloadGithubUserOrgMigrationDataArchiveDownload user_org_migration_test.go:226:1
3 main TestDownloadGithubUserOrgMigrationDataArchiveDownloadFail user_org_migration_test.go:190:1
3 main TestGetUserOwnedOrganizationsNone user_org_migration_test.go:19:1
3 main TestDownloadGithubUserMigrationDataArchiveDownload user_migration_test.go:167:1
3 main TestDownloadGithubUserMigrationDataArchiveDownloadFail user_migration_test.go:132:1
3 main DeleteGithubUserMigration user_data.go:235:1
3 main getGithubUserMigrations user_data.go:198:1
3 main createGithubOrgMigration user_data.go:74:1
3 main TestGetWhitelistGitHubRepositories repositories_test.go:119:1
3 main TestGetStarredGitHubRepositories repositories_test.go:100:1
3 main TestGetPrivateGitHubRepositories repositories_test.go:81:1
3 main TestGetPublicGitHubRepositories repositories_test.go:62:1
3 main validateConfig options.go:80:1
3 main contains helpers.go:56:1
3 main validGitlabProjectMembership helpers.go:46:1
3 main getToken client.go:60:1
3 main startOAuthFlow client.go:24:1
3 main TestBareBackup backup_test.go:71:1
3 main TestBackup backup_test.go:38:1
2 main TestDownloadGithubUserOrgMigrationDataFailed user_org_migration_test.go:163:1
2 main TestCreateGithubUserOrgMigration user_org_migration_test.go:133:1
2 main TestDownloadGithubUserMigrationDataFailed user_migration_test.go:106:1
2 main TestCreateGitHubUserMigrationRetryMax user_migration_test.go:33:1
2 main setupRepositoryTests repositories_test.go:26:1
2 main saveToken client.go:45:1
1 main (*requestCounter).RoundTrip user_migration_test.go:25:1
1 main GetGithubUserMigration user_data.go:222:1
1 main getLocalOrgMigrationFilepath user_data.go:36:1
1 main getLocalMigrationFilepath user_data.go:32:1
1 main teardownRepositoryTests repositories_test.go:54:1
1 main writeExpectedGoldenFile cli_test.go:71:1
1 main fakeRemoteUpdateCommand backup_test.go:30:1
1 main fakeCloneCommand backup_test.go:22:1
1 main fakePullCommand backup_test.go:14:1
1 main createBackupRootDirIfRequired backup.go:107:1

</issue_description>

<agent_instructions>Improve the code for long term maintenance, explaining the why of things you are doing.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Improve code quality #67

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