feat(azure-ai+gpu-ui): per-tenant Azure AI config + GPU health panel

- Per-tenant Azure AI config stored in tenants.tenant_config JSONB
- GET/PUT /api/tenants/{id}/ai-config + POST .../test connection
- api_key never returned to frontend (has_api_key: bool pattern)
- azure_ai.py resolves creds from tenant config when ai_enabled=True
- ai_tasks.py loads tenant config and passes it to validate_thumbnail
- Admin GPU Status section: probe button + status badge + last-checked time
- Notifications: _BELL_CHANNELS filter (notification+alert only in bell)
- Tenants.tsx: per-row Azure AI Config modal with URL auto-parse helper
- Remove duplicate in-memory /gpu-probe endpoints (kept DB-backed /probe/gpu)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/domains/tenants/models.py

@@ -12,6 +12,15 @@ _DEFAULT_TENANT_CONFIG = {
     "fallback_material": "SCHAEFFLER_059999_FailedMaterial",
     "notifications_enabled": True,
     "invoice_prefix": "INV",
+    # Azure AI validation (per-tenant)
+    "ai_enabled": False,
+    "ai_api_key": None,          # stored but never returned to frontend
+    "ai_endpoint": None,         # e.g. https://myinstance.openai.azure.com
+    "ai_deployment": "gpt-4o",
+    "ai_api_version": "2024-02-01",
+    "ai_max_tokens": 500,
+    "ai_temperature": 0.1,
+    "ai_validation_prompt": None,  # None = use DEFAULT_VALIDATION_PROMPT from azure_ai.py
 }