feat(core): reconnect IMAP for ActiveSync mail via mail API

[TDannhauer]

Summary

• On ActiveSync auth and lazily in the IMAP factory, ensure the mail app has a live IMAP connection via the optional mail/ensureImapConnection API method.
• The IMAP factory now throws a clear Horde_ActiveSync_Exception instead of returning an empty client.

Motivation

ActiveSync authenticates to Horde, but with hordeauth mail backends the mail app may not have an established IMAP login on stateless or long-running (PING) requests. $registry->mail->imapOb() then returns an empty client, and Horde_ActiveSync_Imap_Adapter ends up calling status() on null (see horde/ActiveSync#78).

Changes

• Horde_Core_ActiveSync_Driver::authenticate(): after successful Horde auth, call _ensureMailAuthenticated(), which triggers $registry->mail->ensureImapConnection([...]) when email sync is enabled.
• Horde_Core_ActiveSync_Imap_Factory::getImapOb(): if imapOb() yields an empty client, call ensureImapConnection() and retry; throw a clear exception if still unavailable.
• Both call sites are guarded by Registry::hasMethod('mail/ensureImapConnection'), so Core remains agnostic of the concrete mail app and no-ops when the capability is absent.

Dependencies

• Uses the mail/ensureImapConnection API method added in horde/imp feat: OAuthTokenService scope-aware token retrieval #89.

Notes

• The failure is timing/heartbeat-dependent and hard to reproduce deterministically; this is a defensive fix that pairs with the null-client guard in fix(activesync): guard against null IMAP client in _getImapOb() ActiveSync#78.

Test plan

• EAS device with mail sync on a hordeauth backend; confirm mail folders sync after idle/PING without status() on null.
• Install without the mail method: confirm ActiveSync auth still succeeds (no-op).