Fix logic bugs found in third multi-agent review

Medium:
- create_ticket_api.php: environment tags were parsed with explode('][') which
  left brackets on the first/last tag so the whitelist never matched, dropping
  the env tag from the dedup hash — a [production] and [staging] issue with
  otherwise-identical components could collide onto one ticket. Use a
  bracket-aware regex.
- CommentModel::getThreadedCommentsPaged only fetched DIRECT children of root
  comments, so when pagination is active, nested replies at depth 2-3 vanished
  from the thread. Expand replies level-by-level (bounded to depth 3).
- StatsModel::getTicketsByAssignee ignored the visibility filter the rest of the
  stats apply, so a non-admin's "by assignee" widget counted (leaked) confidential
  tickets. Thread the same filter through.
- watch_ticket.php GET path returned watch state / watcher names / count for any
  ticket with no access check (the POST path checks it) — added canUserAccessTicket.
- dashboard.js kanban: every card rendered as P4 because the [class*="lt-p"]
  selector never matched the lt-badge-p1 class and the fallback didn't strip "P".
  Extract the digit directly.

Low:
- audit_log.php CSV: "Log ID" column was always blank ($log['log_id'] vs the real
  audit_id column). Use audit_id.
- check_duplicates.php: the graceful-degradation try/catch only covered the throw
  path; guard the false-return (non-exception mysqli) path too.
- notifications.php: owner-who-is-also-@mentioned got two notifications for one
  comment; drop the duplicate comment row when a mention covers the same comment.
- dashboard.js hover preview rendered "PP1" (doubled prefix); strip the leading P.
- markdown.js: code/inline-code restore used string replace, so $&, $$, $`, $' in
  user code were treated as replacement patterns; use a function replacer. Also
  removed an unused loop var.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

models/CommentModel.php

@@ -176,27 +176,41 @@ class CommentModel
             return [];
         }
 
-        // All replies for these root comments (up to 3 levels deep)
-        $placeholders = implode(',', array_fill(0, count($rootIds), '?'));
-        $replySql = "SELECT tc.*, u.display_name, u.username
-                     FROM ticket_comments tc
-                     LEFT JOIN users u ON tc.user_id = u.user_id
-                     WHERE tc.ticket_id = ?
-                       AND tc.parent_comment_id IN ($placeholders)
-                       AND tc.parent_comment_id IS NOT NULL
-                     ORDER BY tc.created_at ASC";
-        $replyStmt = $this->conn->prepare($replySql);
-        $types = 'i' . str_repeat('i', count($rootIds));
-        $replyStmt->bind_param($types, $ticketId, ...$rootIds);
-        $replyStmt->execute();
-        $replyResult = $replyStmt->get_result();
-        $replyStmt->close();
+        // Load replies level-by-level under this page's roots. A single
+        // "parent_comment_id IN (rootIds)" only fetches DIRECT children, so
+        // grandchildren/great-grandchildren (addComment allows up to depth 3)
+        // would be missing from the map and dropped by buildCommentThread.
+        // Expand iteratively until no new replies (bounded by max depth 3).
+        $parentIds = $rootIds;
+        $depth = 0;
+        while (!empty($parentIds) && $depth < 3) {
+            $placeholders = implode(',', array_fill(0, count($parentIds), '?'));
+            $replySql = "SELECT tc.*, u.display_name, u.username
+                         FROM ticket_comments tc
+                         LEFT JOIN users u ON tc.user_id = u.user_id
+                         WHERE tc.ticket_id = ?
+                           AND tc.parent_comment_id IN ($placeholders)
+                         ORDER BY tc.created_at ASC";
+            $replyStmt = $this->conn->prepare($replySql);
+            $types = 'i' . str_repeat('i', count($parentIds));
+            $replyStmt->bind_param($types, $ticketId, ...$parentIds);
+            $replyStmt->execute();
+            $replyResult = $replyStmt->get_result();
+            $replyStmt->close();
 
-        while ($row = $replyResult->fetch_assoc()) {
-            $row['display_name_formatted'] = $row['display_name'] ?: ($row['user_name'] ?? 'Unknown User');
-            $row['replies']      = [];
-            $row['thread_depth'] = $row['thread_depth'] ?? 1;
-            $commentMap[$row['comment_id']] = $row;
+            $nextParentIds = [];
+            while ($row = $replyResult->fetch_assoc()) {
+                if (isset($commentMap[$row['comment_id']])) {
+                    continue; // guard against cycles / duplicates
+                }
+                $row['display_name_formatted'] = $row['display_name'] ?: ($row['user_name'] ?? 'Unknown User');
+                $row['replies'] = [];
+                $row['thread_depth'] = $depth + 1;
+                $commentMap[$row['comment_id']] = $row;
+                $nextParentIds[] = $row['comment_id'];
+            }
+            $parentIds = $nextParentIds;
+            $depth++;
         }
 
         $rootComments = [];