v0.171.0: disk-health card device-model label (pairs with agent v0.95.0)

agentapi.SmartSummary.ModelName mirrors the agent's model_name; the card row label
prefers the device model over the raw name/UUID, falling back to Name(+hint) on an
old agent. Additive. Test + red-proof (drop fallback -> A4 fails).

controller/internal/agentapi/client.go

@@ -1012,9 +1012,10 @@ type ThinPoolFill struct {
 // The SATA set (reallocated/pending/offline-uncorrectable) and the NVMe set
 // (critical_warning/media_errors/percentage_used) are both carried; a device populates only its own.
 type SmartSummary struct {
-	Health       string `json:"health"` // PASSED | FAILING | UNKNOWN
-	TemperatureC *int   `json:"temperature_c"`
-	PowerOnHours *int   `json:"power_on_hours"`
+	Health       string  `json:"health"`               // PASSED | FAILING | UNKNOWN
+	ModelName    *string `json:"model_name,omitempty"` // smartctl device model (agent v0.95.0+); nil on older agents
+	TemperatureC *int    `json:"temperature_c"`
+	PowerOnHours *int    `json:"power_on_hours"`
 	// SATA attributes.
 	ReallocatedSectors   *int `json:"reallocated_sectors"`
 	PendingSectors       *int `json:"pending_sectors"`