feat: ticket watchers, fulltext search, single-query pagination, watcher notifications

Ticket watchers:
- api/watch_ticket.php: GET (watch state) + POST (watch/unwatch toggle)
- index.php: route for /api/watch_ticket.php
- TicketView: WATCH/UNWATCH button with live state fetch and toggle
- NotificationHelper::notifyWatchers(): fetches watchers from DB, resolves
  Matrix IDs via Synapse, fires notification to watchers + global list
- add_comment.php, update_ticket.php: call notifyWatchers on comment and
  status-change events respectively

Fulltext search:
- TicketModel::hasFulltextIndex(): detects FULLTEXT index via information_schema
- getAllTickets(): uses MATCH...AGAINST when fulltext index exists, LIKE fallback
  when not yet applied — zero-downtime rollout

Single-query pagination:
- getAllTickets() replaces separate COUNT + SELECT with COUNT(*) OVER() window
  function — one round trip to DB per page load instead of two

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

helpers/NotificationHelper.php

@@ -136,6 +136,63 @@ class NotificationHelper {
         ]);
     }
 
+    /**
+     * Notify all watchers of a ticket about an update event.
+     *
+     * Fetches watchers from the DB, resolves their Matrix IDs via Synapse,
+     * and fires the appropriate event notification with them in notify_users.
+     *
+     * @param \mysqli     $conn
+     * @param string|int  $ticketId
+     * @param string      $ticketTitle
+     * @param string      $event        One of: status_changed, comment_added, assigned
+     * @param array       $extraData    Merged into the payload (old_status/new_status, author, etc.)
+     * @param int|null    $excludeUserId  Don't notify the actor themselves
+     */
+    public static function notifyWatchers(\mysqli $conn, $ticketId, string $ticketTitle, string $event, array $extraData = [], ?int $excludeUserId = null): void {
+        $webhookUrl = $GLOBALS['config']['MATRIX_WEBHOOK_URL'] ?? null;
+        $domain     = $GLOBALS['config']['MATRIX_DOMAIN']      ?? null;
+        if (!$webhookUrl || !$domain) {
+            return;
+        }
+
+        // Fetch watcher usernames
+        $sql  = "SELECT u.username FROM ticket_watchers tw JOIN users u ON tw.user_id = u.user_id WHERE tw.ticket_id = ?";
+        $stmt = $conn->prepare($sql);
+        $stmt->bind_param("i", $ticketId);
+        $stmt->execute();
+        $result = $stmt->get_result();
+        $stmt->close();
+
+        $usernames = [];
+        while ($row = $result->fetch_assoc()) {
+            $usernames[] = $row['username'];
+        }
+
+        if (empty($usernames)) {
+            return;
+        }
+
+        // Resolve to Matrix IDs — skip users without Synapse accounts
+        $matrixIds = SynapseHelper::resolveUsernames($usernames);
+        if (empty($matrixIds)) {
+            return;
+        }
+
+        // Remove the global notify list duplicates and build payload
+        $allNotify = array_unique(array_merge($matrixIds, self::notifyUsers()));
+
+        $payload = array_merge($extraData, [
+            'event'        => $event,
+            'ticket_id'    => $ticketId,
+            'title'        => $ticketTitle,
+            'url'          => UrlHelper::ticketUrl($ticketId),
+            'notify_users' => array_values($allNotify),
+        ]);
+
+        self::fire($payload);
+    }
+
     /**
      * Ticket assigned (or reassigned) to a user.
      *