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/DEPLOY.md

@@ -59,6 +59,14 @@ docker compose exec api flask db upgrade
 
 This applies the baseline migration (creates all tables) and any subsequent migrations. Re-running is idempotent.
 
+**Charset:** the schema is utf8mb4 (`utf8mb4_unicode_ci`). The docker-compose `db` service sets `--character-set-server=utf8mb4`, so the auto-created `shopdb_flask` database is utf8mb4. If you point at an external MySQL instead of the bundled container, create the database as utf8mb4 first, or it inherits the server default (often latin1) and the schema silently drifts:
+
+```sql
+CREATE DATABASE shopdb_flask CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+```
+
+`DATABASE_URL` must keep `?charset=utf8mb4` so the connection matches. On MySQL older than 5.7 also enable `innodb_large_prefix=ON` + `innodb_file_format=Barracuda`, or the utf8mb4 indexes exceed the 767-byte prefix limit (error 1071). MySQL 5.7+ and 8.0 need no extra config.
+
 ## Step 4: Seed reference data
 
 ```bash