Rewrite email parser using ImapEngine, harden processing loop

Replace webklex/php-imap with directorytree/imapengine in the ticket
email parser. ImapEngine is pure PHP over sockets.

Parser improvements:
- Wrap per-message processing in try/catch so one malformed email
  can't abort the run; failures are flagged and logged with UID
- Query unseen + unflagged so previously-failed (flagged) messages
  are no longer re-processed on every cron run
- Skip vacation/auto-responder emails (RFC 3834) to prevent mail
  loops with the ticket auto-reply
- Cap messages per run (50) and attachment size (15MB); inline
  images over 2MB are stored as attachments instead of base64-embedded
  in ticket details
- Atomic lock file creation
- preg_quote() the ticket prefix in subject matching
- Dedupe CC watchers and exclude the sender
- Map webklex 'tls' encryption setting to STARTTLS for compatibility

NDR/DSN parsing now walks MIME parts via the underlying
zbateson parser instead of relying on attachment extraction.

plugins/vendor/composer/autoload_files.php

@@ -11,10 +11,16 @@ return array(
     '6e3fae29631ef280660b3cdad06f25a8' => $vendorDir . '/symfony/deprecation-contracts/function.php',
     '606a39d89246991a373564698c2d8383' => $vendorDir . '/symfony/polyfill-php85/bootstrap.php',
     '2203a247e6fda86070a5e4e07aed533a' => $vendorDir . '/symfony/clock/Resources/now.php',
-    '9d2b9fc6db0f153a0a149fefb182415e' => $vendorDir . '/symfony/polyfill-php84/bootstrap.php',
     'a1105708a18b76903365ca1c4aa61b02' => $vendorDir . '/symfony/translation/Resources/functions.php',
+    '9d2b9fc6db0f153a0a149fefb182415e' => $vendorDir . '/symfony/polyfill-php84/bootstrap.php',
+    'e69f7f6ee287b969198c3c9d6777bd38' => $vendorDir . '/symfony/polyfill-intl-normalizer/bootstrap.php',
     '23f09fe3194f8c2f70923f90d6702129' => $vendorDir . '/illuminate/collections/functions.php',
     '60799491728b879e74601d83e38b2cad' => $vendorDir . '/illuminate/collections/helpers.php',
+    'f598d06aa772fa33d905e87be6398fb1' => $vendorDir . '/symfony/polyfill-intl-idn/bootstrap.php',
     'f625ee536139dfb962a398b200bdb2bd' => $vendorDir . '/illuminate/support/functions.php',
     '72579e7bd17821bb1321b87411366eae' => $vendorDir . '/illuminate/support/helpers.php',
+    'a4a119a56e50fbb293281d9a48007e0e' => $vendorDir . '/symfony/polyfill-php80/bootstrap.php',
+    '7b11c4dc42b3b3023073cb14e519683c' => $vendorDir . '/ralouphie/getallheaders/src/getallheaders.php',
+    'def43f6c87e4f8dfd0c9e1b1bab14fe8' => $vendorDir . '/symfony/polyfill-iconv/bootstrap.php',
+    'b33e3d135e5d9e47d845c576147bda89' => $vendorDir . '/php-di/php-di/src/functions.php',
 );