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/schemas.py

@@ -24,3 +24,25 @@ class TenantOut(BaseModel):
     created_at: datetime
 
     model_config = {"from_attributes": True}
+
+
+class TenantAIConfigUpdate(BaseModel):
+    ai_enabled: bool = False
+    ai_endpoint: str | None = None
+    ai_deployment: str = "gpt-4o"
+    ai_api_version: str = "2024-02-01"
+    ai_api_key: str | None = None     # optional — don't require re-entry
+    ai_max_tokens: int = 500
+    ai_temperature: float = 0.1
+    ai_validation_prompt: str | None = None
+
+
+class TenantAIConfigOut(BaseModel):
+    ai_enabled: bool
+    ai_endpoint: str | None
+    ai_deployment: str
+    ai_api_version: str
+    has_api_key: bool              # True if ai_api_key is set — never return the key itself
+    ai_max_tokens: int
+    ai_temperature: float
+    ai_validation_prompt: str | None