Dissolve System Settings into individual settings pages

The monolithic tab page competed with the settings rail as a second
navigation system, and its Integrations tab was a dumping ground. Each
section is now its own routed rail page (ServiceNow, Zabbix Supplies,
Dell Warranty, Collector PC Types, Branding, Floor Map, Printing and
Labels, Email/SMTP, Audit, Authentication, Asset Identifiers, Global
Search), thin over a shared useSystemSettings composable, grouped
logically in the rail with system groups clustered last. Old
/settings/system?tab= URLs redirect to the right page.

Also fixes the post-login redirect: the auth guard now remembers the
intended destination and Login returns there (same-site paths only).

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

frontend/src/views/settings/SettingsLayout.vue

@@ -59,20 +59,11 @@ const visibleGroups = computed(() => {
     .filter(g => g.cards.length)
 })
 
-// A rail link is active when the current path matches its base path
-// (ignoring query, so /settings/system?tab=map and /settings/system stay distinct
-//  only by their own comparison below).
+// A rail link is active when the current path matches its base path.
+// Every settings section is now its own page, so a plain path compare suffices.
 function isActive(to) {
   const base = to.split('?')[0]
-  const query = to.includes('?') ? to.split('?')[1] : ''
-  if (route.path !== base) return false
-  // Floor Map shares /settings/system with System Settings; disambiguate by tab.
-  if (base === '/settings/system') {
-    const wantMap = query.includes('tab=map')
-    const onMap = route.query.tab === 'map'
-    return wantMap === onMap
-  }
-  return true
+  return route.path === base
 }
 </script>