fix(smart v0.1.13): SmartTemp.current optionnel — évite échec parse JSON

Certains NVMe (ASUS TUF A16) ont un champ temperature sans current.
Le champ requis current: i64 faisait crasher toute la désérialisation.
Correction : #[serde(default)] + and_then au lieu de map.

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

agent/src/metrics/smart.rs

@@ -12,7 +12,10 @@ struct SmartJson {
 struct SmartStatus { passed: bool }
 
 #[derive(Deserialize)]
-struct SmartTemp { current: i64 }
+struct SmartTemp {
+    #[serde(default)]
+    current: Option<i64>,
+}
 
 #[derive(Deserialize)]
 struct SmartAttrs { table: Vec<SmartAttr> }
@@ -44,7 +47,7 @@ pub fn is_available() -> bool {
 pub fn parse_json(json: &str) -> Result<crate::payload::SmartMetrics, serde_json::Error> {
     let s: SmartJson = serde_json::from_str(json)?;
 
-    let temperature = s.temperature.as_ref().map(|t| t.current)
+    let temperature = s.temperature.as_ref().and_then(|t| t.current)
         .or_else(|| s.nvme_smart_health_information_log.as_ref()?.temperature);
 
     let mut reallocated = None;