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/directorytree/imapengine/src/Collections/FolderCollection.php

@@ -0,0 +1,11 @@
+<?php
+
+namespace DirectoryTree\ImapEngine\Collections;
+
+use DirectoryTree\ImapEngine\FolderInterface;
+use Illuminate\Support\Collection;
+
+/**
+ * @template-extends Collection<array-key, FolderInterface>
+ */
+class FolderCollection extends Collection {}

plugins/vendor/directorytree/imapengine/src/Collections/MessageCollection.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace DirectoryTree\ImapEngine\Collections;
+
+use DirectoryTree\ImapEngine\Message;
+use DirectoryTree\ImapEngine\MessageInterface;
+
+/**
+ * @template-extends PaginatedCollection<array-key, MessageInterface|Message>
+ */
+class MessageCollection extends PaginatedCollection
+{
+    /**
+     * Find a message by its UID.
+     */
+    public function find(int $uid): ?MessageInterface
+    {
+        return $this->first(
+            fn (MessageInterface $message) => $message->uid() === $uid
+        );
+    }
+
+    /**
+     * Find a message by its UID or throw an exception.
+     */
+    public function findOrFail(int $uid): MessageInterface
+    {
+        return $this->firstOrFail(
+            fn (MessageInterface $message) => $message->uid() === $uid
+        );
+    }
+}

plugins/vendor/directorytree/imapengine/src/Collections/PaginatedCollection.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace DirectoryTree\ImapEngine\Collections;
+
+use DirectoryTree\ImapEngine\Pagination\LengthAwarePaginator;
+use Illuminate\Support\Collection;
+
+/**
+ * @template TKey of array-key
+ * @template TValue
+ *
+ * @template-extends Collection<TKey, TValue>
+ */
+class PaginatedCollection extends Collection
+{
+    /**
+     * The total number of items.
+     */
+    protected int $total = 0;
+
+    /**
+     * Paginate the current collection.
+     *
+     * @return LengthAwarePaginator<TKey, TValue>
+     */
+    public function paginate(int $perPage = 15, ?int $page = null, string $pageName = 'page', bool $prepaginated = false): LengthAwarePaginator
+    {
+        $total = $this->total ?: $this->count();
+
+        $results = ! $prepaginated && $total ? $this->forPage($page, $perPage) : $this;
+
+        return $this->paginator($results, $total, $perPage, $page, $pageName);
+    }
+
+    /**
+     * Create a new length-aware paginator instance.
+     *
+     * @return LengthAwarePaginator<TKey, TValue>
+     */
+    protected function paginator(Collection $items, int $total, int $perPage, ?int $currentPage, string $pageName): LengthAwarePaginator
+    {
+        return new LengthAwarePaginator($items, $total, $perPage, $currentPage, $pageName);
+    }
+
+    /**
+     * Get or set the total amount.
+     */
+    public function total(?int $total = null): ?int
+    {
+        if (is_null($total)) {
+            return $this->total;
+        }
+
+        return $this->total = $total;
+    }
+}

plugins/vendor/directorytree/imapengine/src/Collections/ResponseCollection.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace DirectoryTree\ImapEngine\Collections;
+
+use DirectoryTree\ImapEngine\Connection\Responses\ContinuationResponse;
+use DirectoryTree\ImapEngine\Connection\Responses\TaggedResponse;
+use DirectoryTree\ImapEngine\Connection\Responses\UntaggedResponse;
+use Illuminate\Support\Collection;
+
+/**
+ * @template TKey of array-key
+ *
+ * @template-covariant TValue
+ *
+ * @extends Collection<array-key, TValue>
+ */
+class ResponseCollection extends Collection
+{
+    /**
+     * Filter the collection to only tagged responses.
+     *
+     * @return self<array-key, TaggedResponse>
+     */
+    public function tagged(): self
+    {
+        return $this->whereInstanceOf(TaggedResponse::class);
+    }
+
+    /**
+     * Filter the collection to only untagged responses.
+     *
+     * @return self<array-key, UntaggedResponse>
+     */
+    public function untagged(): self
+    {
+        return $this->whereInstanceOf(UntaggedResponse::class);
+    }
+
+    /**
+     * Filter the collection to only continuation responses.
+     *
+     * @return self<array-key, ContinuationResponse>
+     */
+    public function continuation(): self
+    {
+        return $this->whereInstanceOf(ContinuationResponse::class);
+    }
+}