feat(tickets): création d'un assistant IA de ticket (backend + frontend)

Ajoute le chat assistant IA attaché à un ticket (#8).

Backend Rust :
- use cases OpenTicketAssistant/CloseTicketAssistant + tests
- politique d'outils par agent (domain/agent_tool_policy) et policy MCP
- store de contexte assistant + gabarit default_ticket_assistant.md + tests
- events TicketAssistantOpened/Closed
- commandes Tauri open_ticket_chat/close_ticket_chat et câblage state/lib/events

Frontend :
- gateway (ports, adapters ticket + mock, domain)
- hook useTicketAssistant + composant TicketAssistantPanel
- intégration dans TicketDetail

Tests verts : vitest tickets.test.tsx (23), cargo test application::ticket_assistant (1),
infrastructure::assistant_context_store (2).

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

crates/app-tauri/src/events.rs

@@ -50,6 +50,20 @@ pub enum DomainEventDto {
         /// Exit code.
         code: i32,
     },
+    /// A ticket assistant chat was opened.
+    #[serde(rename_all = "camelCase")]
+    TicketAssistantOpened {
+        /// Bound ticket reference.
+        issue_ref: String,
+        /// Runtime profile id.
+        profile_id: String,
+    },
+    /// A ticket assistant chat was closed.
+    #[serde(rename_all = "camelCase")]
+    TicketAssistantClosed {
+        /// Bound ticket reference.
+        issue_ref: String,
+    },
     /// An agent's busy/idle state changed (cadrage C4 §4.2). The frontend dims
     /// "Envoyer" while `busy` is `true`.
     #[serde(rename_all = "camelCase")]
@@ -551,6 +565,16 @@ impl From<&DomainEvent> for DomainEventDto {
                 agent_id: agent_id.to_string(),
                 code: *code,
             },
+            DomainEvent::TicketAssistantOpened {
+                issue_ref,
+                profile_id,
+            } => Self::TicketAssistantOpened {
+                issue_ref: issue_ref.to_string(),
+                profile_id: profile_id.to_string(),
+            },
+            DomainEvent::TicketAssistantClosed { issue_ref } => Self::TicketAssistantClosed {
+                issue_ref: issue_ref.to_string(),
+            },
             DomainEvent::AgentBusyChanged { agent_id, busy } => Self::AgentBusyChanged {
                 agent_id: agent_id.to_string(),
                 busy: *busy,
@@ -1081,4 +1105,24 @@ mod tests {
         assert_eq!(json["to"], to.to_string());
         assert_eq!(json["version"], 3);
     }
+
+    #[test]
+    fn ticket_assistant_events_relay_to_dto_and_wire() {
+        let profile_id = domain::ProfileId::from_uuid(uuid::Uuid::from_u128(9));
+        let opened = DomainEventDto::from(&DomainEvent::TicketAssistantOpened {
+            issue_ref: domain::IssueRef::from(domain::IssueNumber::new(7).unwrap()),
+            profile_id,
+        });
+        let opened = serde_json::to_value(&opened).expect("serialisable");
+        assert_eq!(opened["type"], "ticketAssistantOpened");
+        assert_eq!(opened["issueRef"], "#7");
+        assert_eq!(opened["profileId"], profile_id.to_string());
+
+        let closed = DomainEventDto::from(&DomainEvent::TicketAssistantClosed {
+            issue_ref: domain::IssueRef::from(domain::IssueNumber::new(7).unwrap()),
+        });
+        let closed = serde_json::to_value(&closed).expect("serialisable");
+        assert_eq!(closed["type"], "ticketAssistantClosed");
+        assert_eq!(closed["issueRef"], "#7");
+    }
 }