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/utils/cmmc_usb_db.py

@@ -0,0 +1,22 @@
+"""Connection helper for the CMMC USB check-in/out database.
+
+Credentials are pulled from app config (env-backed, see Config.CMMC_USB_DB_*),
+never hardcoded. Used by the USB plugin to track device check-in/out against a
+separate MySQL database (cmmc_usb), mirroring the read-only employee-directory
+pattern in employee_db.py. Unlike the employee DB this one is read-write, so
+callers commit their own writes and close the connection in a finally block.
+"""
+
+import pymysql
+from flask import current_app
+
+
+def cmmc_usb_connection():
+    """Open a pymysql connection to the cmmc_usb DB."""
+    return pymysql.connect(
+        host=current_app.config['CMMC_USB_DB_HOST'],
+        user=current_app.config['CMMC_USB_DB_USER'],
+        password=current_app.config['CMMC_USB_DB_PASSWORD'],
+        database=current_app.config['CMMC_USB_DB_NAME'],
+        cursorclass=pymysql.cursors.DictCursor,
+    )