feat(model-server): afficher le téléchargement du modèle llamacpp au démarrage (#54)

Ajoute un handle du téléchargement des modèles lors du démarrage de
llamacpp : le domaine et l'application émettent la progression de
téléchargement du modèle, relayée en événement côté app-tauri, et l'UI
l'affiche via un badge de lancement et un overlay de cellule pendant que
le serveur de modèle démarre.

Backend (B1) : progression de téléchargement dans domain/application,
relais d'événement app-tauri, couverture de tests.
Frontend (F1) : modelServerLaunch, badge et overlay LayoutGrid, tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/app-tauri/src/events.rs

@@ -36,6 +36,18 @@ pub enum ModelServerStatusDto {
     Probing,
     /// IdeA is starting the process.
     Starting,
+    /// Server is downloading/preparing a remote model.
+    #[serde(rename_all = "camelCase")]
+    Downloading {
+        /// Downloaded bytes when known.
+        downloaded_bytes: Option<u64>,
+        /// Total bytes when known.
+        total_bytes: Option<u64>,
+        /// Completion percentage when known.
+        percent: Option<f32>,
+        /// Remote model source.
+        source: Option<String>,
+    },
     /// Server is ready.
     #[serde(rename_all = "camelCase")]
     Ready {
@@ -58,6 +70,17 @@ impl From<&ModelServerLifecycleStatus> for ModelServerStatusDto {
             ModelServerLifecycleStatus::NotConfigured => Self::NotConfigured,
             ModelServerLifecycleStatus::Probing => Self::Probing,
             ModelServerLifecycleStatus::Starting => Self::Starting,
+            ModelServerLifecycleStatus::Downloading {
+                downloaded_bytes,
+                total_bytes,
+                percent,
+                source,
+            } => Self::Downloading {
+                downloaded_bytes: *downloaded_bytes,
+                total_bytes: *total_bytes,
+                percent: *percent,
+                source: source.clone(),
+            },
             ModelServerLifecycleStatus::Ready { reused } => Self::Ready { reused: *reused },
             ModelServerLifecycleStatus::Failed { code, message } => Self::Failed {
                 code: code.clone(),
@@ -1168,6 +1191,31 @@ mod tests {
         assert_eq!(json["status"]["reused"], true);
     }
 
+    #[test]
+    fn model_server_status_changed_relays_downloading_to_dto_and_wire() {
+        let dto = DomainEventDto::from(&DomainEvent::ModelServerStatusChanged {
+            server_id: server(37),
+            status: ModelServerLifecycleStatus::Downloading {
+                downloaded_bytes: None,
+                total_bytes: None,
+                percent: None,
+                source: Some("Qwen/Qwen3-Coder-30B-A3B-Instruct-GGUF".to_owned()),
+            },
+        });
+
+        let json = serde_json::to_value(&dto).expect("serialisable");
+        assert_eq!(json["type"], "modelServerStatusChanged");
+        assert_eq!(json["serverId"], server(37).to_string());
+        assert_eq!(json["status"]["state"], "downloading");
+        assert_eq!(json["status"]["downloadedBytes"], serde_json::Value::Null);
+        assert_eq!(json["status"]["totalBytes"], serde_json::Value::Null);
+        assert_eq!(json["status"]["percent"], serde_json::Value::Null);
+        assert_eq!(
+            json["status"]["source"],
+            "Qwen/Qwen3-Coder-30B-A3B-Instruct-GGUF"
+        );
+    }
+
     #[test]
     fn agent_launch_failed_relays_model_server_cause() {
         let dto = DomainEventDto::from(&DomainEvent::AgentLaunchFailed {