feat(sync): evict ghost items via deferred synthetic deletions

[TDannhauer]

Summary

• Self-heal "ghost" items: mail a client may still hold although it was
  deleted server-side long ago and the client never applied the Remove.
• Detection at Fetch time, eviction deferred through the regular change
  pipeline (never in the Fetch response itself).

Motivation

When a mail is deleted via IMAP/webmail, the server sends a Remove once.
If the client fails to apply it (observed with iOS Mail), the client
retries SYNC_FETCH for the vanished item indefinitely; the diff engine
can never delete an untracked uid again, so the loop never ends.
Answering with Status 8 alone does not recover iOS.

An earlier variant that emitted the Remove in the same Sync response as
the Fetch reply reproducibly crashed iOS maild (SIGABRT parsing
assertion, crash loop with 20-minute throttling). Hence the deferred
design: record the ghost uid, deliver the Remove in a normal GetChanges
response — the shape every client already handles.

Changes

• Exporter_Sync::fetchIds() records NotFound failures;
  getFailedFetchIds() exposes them.
• Request_Sync::_getGhostFetchIds() filters failures to uids untracked
  in the folder state and records them via State_Base::addGhostUids().
• Folder_Imap persists ghost uids (new optional g key, BC in both
  directions) with add/list/remove API.
• State_Base::getChanges() injects synthetic CHANGE_TYPE_DELETE
  entries for recorded ghosts (also in PING mode, so the device is woken
  to pick up the eviction); the uid is cleared once the deletion is
  exported. Uids tracked again in state are dropped without eviction.

Expected exception types

No new catch blocks; existing Horde_Exception_NotFound handling in
fetchIds() is reused.

Test plan

• 16 new unit tests (exporter failure tracking, folder ghost API and
  serialization, ghost detection, state injection/clearing)
• Full package suite: no new failures
• Verified live: iOS device recovered, ghost item evicted, fetch
  loop ended

[github-actions]

🔍 CI Results

Overall: ❌ 12/12 lanes failed

TL;DR: ❌ Quality issues: PHPStan: 242 unique errors in 11 lanes; PHP-CS-Fixer: 25 files.

Summary by PHP Version

PHP	dev	stable
8.0	❌	❌
8.1	❌	❌
8.2	❌	❌
8.3	❌	❌
8.4	❌	❌
8.5	❌	❌

Quality Metrics

• PHPUnit: did not run (11 lanes exited non-zero with no test output) ❌
• PHPStan (advisory): 242 unique errors in 11 lanes ⚠️
• PHP-CS-Fixer: 25 unique files with issues (of 206 checked) ⚠️

❌ Failed Lanes

php8.0-dev

• PHPUnit: 0 failures, 0 errors

php8.0-stable

• PHPUnit: ❌ Setup failed (Composer install failed in /tmp/horde-ci/lanes/php8.0-stable/ActiveSync: Your requirements could not be resolved to an installable set of packages.)
• PHPStan: ❌ Setup failed (Composer install failed in /tmp/horde-ci/lanes/php8.0-stable/ActiveSync: Your requirements could not be resolved to an installable set of packages.)

php8.1-dev

• PHPUnit: 0 failures, 0 errors

php8.1-stable

• PHPUnit: 0 failures, 0 errors

php8.2-dev

• PHPUnit: 0 failures, 0 errors

php8.2-stable

• PHPUnit: 0 failures, 0 errors

php8.3-dev

• PHPUnit: 0 failures, 0 errors

php8.3-stable

• PHPUnit: 0 failures, 0 errors

php8.4-dev

• PHPUnit: 0 failures, 0 errors
• PHP-CS-Fixer: 25 files with issues

php8.4-stable

• PHPUnit: 0 failures, 0 errors

php8.5-dev

• PHPUnit: 0 failures, 0 errors

php8.5-stable

• PHPUnit: 0 failures, 0 errors

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