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>

docs/adr/ADR-004-deployment-topology.md

@@ -21,7 +21,12 @@ The codebase today is single-tenant per deployment. There is no `siteid` column,
 
 Each site:
 
-- Owns its database (own credentials, own backup policy, own retention)
+- Owns its database (own credentials, own backup policy, own retention). The
+  database charset is part of the contract: it must be **utf8mb4**
+  (`utf8mb4_unicode_ci`). The migration chain creates every table utf8mb4, and
+  the connection pins `?charset=utf8mb4`. A site that creates the database with
+  a different default charset (older MySQL defaults to latin1) gets a schema
+  that silently diverges from every other site. See `docs/DEPLOY.md`.
 - Picks its own enabled plugins
 - Configures its own JWT secret, CORS allowlist, Zabbix integration, Active Directory binding
 - Deploys at its own cadence