feat(workstate): résumés de conversation dans le read-model (Lot C backend)

Étend le read-model work-state pour exposer un résumé par conversation
(participants, dernier message/activité, compteurs) câblé jusqu'au DTO
camelCase de l'état app-tauri.

- application : assemblage des résumés de conversation dans le work-state.
- app-tauri : DTO camelCase des résumés + exposition dans l'état.

Tests verts : application workstate (21), app-tauri dto_agents (21),
aucun warning Rust.

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

crates/app-tauri/tests/dto_agents.rs

@@ -222,6 +222,7 @@ fn project_work_state_dto_serialises_live_and_busy_camelcase() {
             },
             tickets: vec![],
         }],
+        conversations: vec![],
     });
 
     let v = serde_json::to_value(&dto).unwrap();
@@ -279,6 +280,7 @@ fn project_work_state_dto_serialises_tickets_camelcase() {
                 },
             ],
         }],
+        conversations: vec![],
     });
 
     let v = serde_json::to_value(&dto).unwrap();
@@ -304,6 +306,80 @@ fn project_work_state_dto_serialises_tickets_camelcase() {
     assert_eq!(next["requesterLabel"], "User");
 }
 
+#[test]
+fn project_work_state_dto_serialises_conversations_camelcase() {
+    use application::{
+        ConversationPreviewStatus, ConversationTurnWorkPreview, ConversationWorkSummary,
+    };
+    use domain::{ConversationId, TurnId, TurnRole};
+
+    let requester = AgentId::from_uuid(Uuid::from_u128(20));
+    let ready_conv = ConversationId::from_uuid(Uuid::from_u128(40));
+    let missing_conv = ConversationId::from_uuid(Uuid::from_u128(41));
+    let up_to = TurnId::from_uuid(Uuid::from_u128(50));
+
+    let dto = app_tauri_lib::dto::ProjectWorkStateDto::from(ProjectWorkState {
+        agents: vec![],
+        conversations: vec![
+            ConversationWorkSummary {
+                conversation_id: ready_conv,
+                status: ConversationPreviewStatus::Ready,
+                objective_preview: Some("Livrer le lot C".to_owned()),
+                summary_preview: Some("Résumé du fil".to_owned()),
+                summary_len: 1024,
+                up_to: Some(up_to),
+                recent_turns: vec![],
+            },
+            ConversationWorkSummary {
+                conversation_id: missing_conv,
+                status: ConversationPreviewStatus::Missing,
+                objective_preview: None,
+                summary_preview: None,
+                summary_len: 0,
+                up_to: None,
+                recent_turns: vec![ConversationTurnWorkPreview {
+                    role: TurnRole::Prompt,
+                    source: TicketWorkSource::Agent {
+                        agent_id: requester,
+                    },
+                    at_ms: 1_700,
+                    text_preview: "Analyse le module".to_owned(),
+                    text_len: 17,
+                }],
+            },
+        ],
+    });
+
+    let v = serde_json::to_value(&dto).unwrap();
+    let ready = &v["conversations"][0];
+    assert_eq!(ready["conversationId"], ready_conv.to_string());
+    assert_eq!(ready["status"], "ready");
+    assert_eq!(ready["objectivePreview"], "Livrer le lot C");
+    assert_eq!(ready["summaryPreview"], "Résumé du fil");
+    assert_eq!(ready["summaryLen"], 1024);
+    assert_eq!(ready["upTo"], up_to.to_string());
+    assert_eq!(ready["recentTurns"], json!([]));
+    // No snake_case leak.
+    assert!(ready.get("conversation_id").is_none());
+    assert!(ready.get("summary_preview").is_none());
+    assert!(ready.get("up_to").is_none());
+
+    let missing = &v["conversations"][1];
+    assert_eq!(missing["status"], "missing");
+    // Absent previews surface as null (predictable, not omitted).
+    assert!(missing["summaryPreview"].is_null());
+    assert!(missing["upTo"].is_null());
+    let turn = &missing["recentTurns"][0];
+    assert_eq!(turn["role"], "prompt");
+    assert_eq!(turn["source"]["kind"], "agent");
+    assert_eq!(turn["source"]["agentId"], requester.to_string());
+    assert_eq!(turn["atMs"], 1_700);
+    assert_eq!(turn["textPreview"], "Analyse le module");
+    assert_eq!(turn["textLen"], 17);
+    assert!(turn.get("at_ms").is_none());
+    assert!(turn.get("text_preview").is_none());
+}
+
 #[test]
 fn launch_agent_request_carries_conversation_id_for_resume() {
     let raw = json!({