Implement getMailboxes API and create dedicated admin section for provider accounts

[Copilot]

The IonosProviderFacade::getMailboxes() method was stubbed out, returning an empty array with a TODO comment. This implements the actual functionality using the IONOS Mail Configuration API and creates a dedicated admin section for email provider account management.

Changes

IonosAccountQueryService

• Added getAllMailAccountResponses() calling $apiInstance->getAllFunctionalAccounts(BRAND, externalReference)
• Returns MailAccountResponse[] from API, empty array on exceptions

IonosProviderFacade

• getMailboxes() now fetches from API via query service
• Transforms responses to required format: array{userId: string, email: string, name: string}
• Extracts userId from email localpart (before @)
• Falls back to userId when getName() returns null

Admin Settings Architecture

• Created ProviderAccountOverviewSettings as dedicated delegated settings class
• Created MailProviderAccountsSection for custom admin navigation entry
• Moved MailboxAdministration UI to separate settings page with own navigation entry
• Email provider account management now appears in its own "Email Provider Accounts" section instead of being embedded in Groupware
• Added webpack entry point provider-account-overview for new settings page
• Registered new settings and section in appinfo/info.xml

Tests

• 5 tests in IonosProviderFacadeTest covering success, empty, exception, and null-name cases
• 3 tests in new IonosAccountQueryServiceTest for API error handling
• 5 tests in new ProviderAccountOverviewSettingsTest for settings class
• 4 tests in new MailProviderAccountsSectionTest for section class

Example

// API returns
[
  MailAccountResponse { email: "john.doe@ionos.com", name: "John Doe" },
  MailAccountResponse { email: "jane@ionos.com", name: null }
]

// Transforms to
[
  ['userId' => 'john.doe', 'email' => 'john.doe@ionos.com', 'name' => 'John Doe'],
  ['userId' => 'jane', 'email' => 'jane@ionos.com', 'name' => 'jane']
]

Backward compatible - returns empty array on API failures with error logging.

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[bromiesTM]

@copilot
Currently the email provider list is displayed in "Groupware.

We have to ensure that:

the Provider emails editing will get its own Admin navigation entry.
Email Provider Settings will get its own delegated settings (e.g. lib/Settings/ProviderAccountOverviewSettings.php)

Use the IDelegatedSettings getSection() to set the Nav Entry

[Copilot]

@copilot
Currently the email provider list is displayed in "Groupware.

...

Done! I've created a separate admin navigation entry for Email Provider Account management:

Changes in commit e06c426:

• Created ProviderAccountOverviewSettings as a separate delegated settings class
• Created MailProviderAccountsSection that returns mail-provider-accounts as the section ID
• Moved the MailboxAdministration UI to the new dedicated settings page
• Registered both the settings and section in info.xml
• Removed MailboxAdministration from the Groupware section

The email provider settings now have their own navigation entry in the admin panel, completely separate from Groupware.