Add an osTicket integration: list open tickets from its database

osTicket's own REST API only supports creating tickets, not listing or
reading them, so this reads osTicket's MySQL/MariaDB database directly
with a read-only user instead - the only integration in this app that
isn't a REST API. Joins the ticket, status, priority, department,
staff, team, and user tables, filtered to tickets in the "open" state
(status names are customizable per install, but that state flag isn't).

Surfaces per-ticket subject, priority, department, assignee, requester,
and osTicket's own overdue/awaiting-reply flags, plus a page at
/osticket and a Dashboard widget with open/overdue/awaiting-reply
counts.

Not verified against a live instance: unlike the HTTP-based
integrations, there was no way to fake a MySQL server to test against
in this environment, so the query is built from osTicket's published
schema but has never actually run against a real database. See
INTEGRATIONS.md for the read-only grant needed and further caveats.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/layout/AppShell.tsx

@@ -29,6 +29,7 @@ import {
   IconRefresh,
   IconActivityHeartbeat,
   IconShieldCheck,
+  IconTicket,
 } from "@tabler/icons-react";
 import { api, type CurrentUser, type MaintenanceWindow } from "../api/client";
 import { formatRemaining } from "../utils/duration";
@@ -99,6 +100,7 @@ const NAV: NavEntry[] = [
     items: [
       { to: "/maintenance", label: "Maintenance", icon: <IconTool size={20} /> },
       { to: "/uptime-kuma", label: "Uptime Kuma", icon: <IconActivityHeartbeat size={20} /> },
+      { to: "/osticket", label: "osTicket", icon: <IconTicket size={20} /> },
       { to: "/generator", label: "Generator", icon: <IconWand size={20} /> },
     ],
   },