Wizard: choose "create tables here" vs "connect your own database" per plugin

Answers the confusion of asking for a DB connection while also offering to
create the tables. Each self-host-capable plugin (employees, usb) now shows a
mode choice; the external connection fields appear only for "connect your own
database". Default is self-hosted (create tables here) - the external path is
the niche/our-site option.

- provisioning_note gains mode_setting; employee_directory_mode + usb_directory_
  mode settings (both default 'selfhosted').
- Wizard renders the radio, shows the note for self-hosted and the config fields
  for external, and saves the chosen mode.

Employees works fully in both modes. USB self-hosted ROUTING is still TODO - the
USB routes read the external cmmc_usb schema; wiring them to the app-owned
tables is the remaining work (tracked).

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

shopdb/core/api/settings.py

@@ -265,10 +265,17 @@ def build_default_settings():
         },
         {
             'key': 'employee_directory_mode',
-            'value': 'external',
+            'value': 'selfhosted',
             'valuetype': 'string',
             'category': 'site',
-            'description': "Employee directory source: 'external' (a separate HR database) or 'selfhosted' (managed in-app under Employees)"
+            'description': "Employee directory source: 'selfhosted' (tables in this app, default) or 'external' (a separate HR database)"
+        },
+        {
+            'key': 'usb_directory_mode',
+            'value': 'selfhosted',
+            'valuetype': 'string',
+            'category': 'site',
+            'description': "USB check-in/out source: 'selfhosted' (tables in this app, default) or 'external' (a separate cmmc_usb database)"
         },
         {
             'key': 'site_base_url',