tenancy: runtime Solo/Hub mode + mode-aware /admin (Phase 1)
Admin can switch live between modes in Admin -> Settings:
- solo: exactly one site (the primary/owner site), no /sites routing, leaner /admin.
- hub: main site + /sites/:slug routing (company; /gebruikers + assignment flow = Phase 2).
Switching is non-destructive (hides only, deletes nothing).
- app_settings (key/value singleton) + SettingsService (cached getTenancy/setTenancy).
- resolveSite: solo pins to the primary site + disables /sites/:slug + host mapping.
- /admin/settings (god-only) toggle; /admin dashboard rewritten, mode-aware.
Tested on the demo: solo/hub dashboard tiles, /sites routing per mode, toggle back/forth.
Co-Authored-By: Claude <noreply@…>