fix(config): prevent card text overflow; fix(onboarding): persist completion server-side

Cards/Grid:
- Add min-width:0 to .device-grid to prevent grid overflow
- Add max-width:100%, overflow:hidden, word-break:break-word to .device-card
- Add min-width:0 and overflow-wrap to .device-card__body
- Bump config.css cache-bust to v=2

Onboarding:
- Add GET/POST /pos/api/config/onboarding-status endpoints in config_bp.py
- onboarding.js now checks server first before showing wizard
- On finish, POSTs completion to server (tenant_config table)
- Falls back to localStorage for fast path and offline resilience
- Bump onboarding.js cache-bust to v=2 in catalog.html

pos/static/css/config.css

@@ -1029,6 +1029,7 @@
       display: grid;
       grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
       gap: var(--space-4);
+      min-width: 0;
     }
 
     .device-card {
@@ -1042,7 +1043,10 @@
       box-shadow: var(--shadow-sm);
       transition: var(--transition-normal);
       min-width: 0;
+      max-width: 100%;
+      overflow: hidden;
       overflow-wrap: break-word;
+      word-break: break-word;
     }
 
     [data-theme="modern"] .device-card {