Add custom fields + warranty plugin, rework settings into two-pane shell

Feature work from the 2026-07 session:

Settings IA
- Replace the flat 27-card settings hub with a persistent two-pane shell
  (SettingsLayout.vue): grouped, searchable left rail + content pane.
- Nest all settings/* routes under the shell via router post-processing;
  shared nav catalog in settingsNav.js. Group by asset class (PCs, Printers,
  Equipment, Network) so per-type settings stop scattering.

Custom fields (core)
- customfields + customfieldvalues tables (migration 7d14), CRUD API at
  /api/customfields, per-asset value get/save.
- Settings management page + reusable CustomFieldsSection (detail) and
  CustomFieldsInputs (form) wired into all four asset types.

Warranty (new plugin)
- plugins/warranty: warranties + warrantyassets (migration 7d15), derived
  coverage status, provider abstraction (manual now; Dell/Lenovo/HP stubs).
- API CRUD + per-asset panel + report buckets; WarrantyPanel on all four
  detail pages; Warranties management page; Warranty report + Reports card.
- Seed warranty.* permissions.

Printer drivers
- printerdrivers table (migration 7d13) linked to printer models; drivers now
  surface on the matching printer's detail page.

Other
- PCDetail rebalanced (Network + Status + Warranty + custom fields on the right).
- Rename PCs list "Features" column to "Remote Access"; fix badge hover underline.
- Drop equipment islocationonly field.
- Centralize asset-type label/route maps into utils/assetTypes.js.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/views/AppLayout.vue

@@ -77,7 +77,7 @@ import { ref, onMounted } from 'vue'
 import { useRouter } from 'vue-router'
 import {
   Sun, Moon, LayoutDashboard, Calendar, Map, Cog, Monitor,
-  Printer, Globe, Usb, AppWindow, BookOpen, BarChart3, Bell
+  Printer, Globe, Usb, AppWindow, BookOpen, BarChart3, Bell, Image, ShieldCheck
 } from 'lucide-vue-next'
 import { useAuthStore } from '../stores/auth'
 import { currentTheme, toggleTheme } from '../stores/theme'
@@ -103,6 +103,8 @@ const iconMap = {
   'app-window': AppWindow,
   'book-open': BookOpen,
   'bar-chart-3': BarChart3,
+  'image': Image,
+  'shield': ShieldCheck,
 }
 
 // Default navigation (used as fallback if API fails)