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>

shopdb/core/models/user.py

@@ -75,6 +75,16 @@ class Permission(db.Model):
         ('notifications.create', 'Create notifications', 'notifications'),
         ('notifications.edit', 'Edit notifications', 'notifications'),
         ('notifications.delete', 'Delete notifications', 'notifications'),
+        # USB devices
+        ('usb.view', 'View USB devices', 'usb'),
+        ('usb.create', 'Create USB devices', 'usb'),
+        ('usb.edit', 'Edit USB devices', 'usb'),
+        ('usb.delete', 'Delete USB devices', 'usb'),
+        # Warranty
+        ('warranty.view', 'View warranties', 'warranty'),
+        ('warranty.create', 'Create warranties', 'warranty'),
+        ('warranty.edit', 'Edit warranties', 'warranty'),
+        ('warranty.delete', 'Delete warranties', 'warranty'),
         # Reports
         ('reports.view', 'View reports', 'reports'),
         ('reports.export', 'Export reports', 'reports'),