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>

api/watch_ticket.php

@@ -0,0 +1,100 @@
+<?php
+/**
+ * Watch / Unwatch Ticket API
+ *
+ * GET  ?ticket_id=N  → returns { watching: bool, watcher_count: int }
+ * POST { ticket_id, action: 'watch'|'unwatch' } → toggles watcher row
+ */
+require_once __DIR__ . '/bootstrap.php';
+require_once dirname(__DIR__) . '/models/TicketModel.php';
+
+$ticketId = isset($_GET['ticket_id'])
+    ? (int)$_GET['ticket_id']
+    : (isset($data['ticket_id']) ? (int)$data['ticket_id'] : 0);
+
+if ($_SERVER['REQUEST_METHOD'] === 'POST') {
+    $data     = json_decode(file_get_contents('php://input'), true) ?? [];
+    $ticketId = (int)($data['ticket_id'] ?? 0);
+    $action   = $data['action'] ?? '';
+
+    if ($ticketId <= 0 || !in_array($action, ['watch', 'unwatch'], true)) {
+        http_response_code(400);
+        echo json_encode(['success' => false, 'error' => 'Invalid parameters']);
+        exit;
+    }
+
+    $ticketModel = new TicketModel($conn);
+    $ticket = $ticketModel->getTicketById($ticketId);
+    if (!$ticket || !$ticketModel->canUserAccessTicket($ticket, $currentUser)) {
+        http_response_code(404);
+        echo json_encode(['success' => false, 'error' => 'Ticket not found']);
+        exit;
+    }
+
+    if ($action === 'watch') {
+        $stmt = $conn->prepare(
+            "INSERT IGNORE INTO ticket_watchers (ticket_id, user_id) VALUES (?, ?)"
+        );
+        $stmt->bind_param("ii", $ticketId, $userId);
+        $stmt->execute();
+        $stmt->close();
+    } else {
+        $stmt = $conn->prepare(
+            "DELETE FROM ticket_watchers WHERE ticket_id = ? AND user_id = ?"
+        );
+        $stmt->bind_param("ii", $ticketId, $userId);
+        $stmt->execute();
+        $stmt->close();
+    }
+
+    // Return updated state
+    $countStmt = $conn->prepare(
+        "SELECT COUNT(*) as cnt FROM ticket_watchers WHERE ticket_id = ?"
+    );
+    $countStmt->bind_param("i", $ticketId);
+    $countStmt->execute();
+    $count = (int)$countStmt->get_result()->fetch_assoc()['cnt'];
+    $countStmt->close();
+
+    echo json_encode([
+        'success'       => true,
+        'watching'      => $action === 'watch',
+        'watcher_count' => $count,
+    ]);
+    exit;
+}
+
+// GET — return current watch state for this user
+if ($_SERVER['REQUEST_METHOD'] !== 'GET') {
+    http_response_code(405);
+    echo json_encode(['success' => false, 'error' => 'Method not allowed']);
+    exit;
+}
+
+if ($ticketId <= 0) {
+    http_response_code(400);
+    echo json_encode(['success' => false, 'error' => 'ticket_id required']);
+    exit;
+}
+
+$watchingStmt = $conn->prepare(
+    "SELECT COUNT(*) as cnt FROM ticket_watchers WHERE ticket_id = ? AND user_id = ?"
+);
+$watchingStmt->bind_param("ii", $ticketId, $userId);
+$watchingStmt->execute();
+$watching = (bool)$watchingStmt->get_result()->fetch_assoc()['cnt'];
+$watchingStmt->close();
+
+$countStmt = $conn->prepare(
+    "SELECT COUNT(*) as cnt FROM ticket_watchers WHERE ticket_id = ?"
+);
+$countStmt->bind_param("i", $ticketId);
+$countStmt->execute();
+$count = (int)$countStmt->get_result()->fetch_assoc()['cnt'];
+$countStmt->close();
+
+echo json_encode([
+    'success'       => true,
+    'watching'      => $watching,
+    'watcher_count' => $count,
+]);