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/tickets.rs

@@ -14,15 +14,16 @@ use tauri::State;
 use uuid::Uuid;
 
 use application::{
-    AppError, AssignIssueAgentInput, AssignTicketToSprintInput, CreateIssueInput,
-    CreateSprintInput, DeleteSprintInput, LinkIssuesInput, ListIssuesInput, ListSprintsInput,
-    OpenProjectInput, ReadIssueCarnetInput, ReadIssueInput, RenameSprintInput, ReorderSprintsInput,
-    UnassignTicketFromSprintInput, UnlinkIssuesInput, UpdateIssueCarnetInput, UpdateIssueInput,
+    AppError, AssignIssueAgentInput, AssignTicketToSprintInput, CloseTicketAssistantInput,
+    CreateIssueInput, CreateSprintInput, DeleteSprintInput, LinkIssuesInput, ListIssuesInput,
+    ListSprintsInput, OpenProjectInput, OpenTicketAssistantInput, ReadIssueCarnetInput,
+    ReadIssueInput, RenameSprintInput, ReorderSprintsInput, UnassignTicketFromSprintInput,
+    UnlinkIssuesInput, UpdateIssueCarnetInput, UpdateIssueInput,
 };
 use domain::{
     AgentId, AgentIssueRole, Issue, IssueActor, IssueCarnet, IssueIndexEntry, IssueLink,
-    IssueLinkKind, IssueListFilter, IssuePriority, IssueRef, IssueStatus, IssueVersion, Project,
-    ProjectId, SprintId, SprintStatus, SprintVersion,
+    IssueLinkKind, IssueListFilter, IssuePriority, IssueRef, IssueStatus, IssueVersion, ProfileId,
+    Project, ProjectId, SprintId, SprintStatus, SprintVersion,
 };
 use infrastructure::{TicketToolError, TicketToolProvider};
 
@@ -106,6 +107,29 @@ pub struct SprintListDto {
     pub items: Vec<SprintDto>,
 }
 
+#[derive(Debug, Clone, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct OpenTicketChatRequestDto {
+    pub project_id: String,
+    pub issue_ref: String,
+    pub profile_id: String,
+}
+
+#[derive(Debug, Clone, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct CloseTicketChatRequestDto {
+    pub project_id: String,
+    pub issue_ref: String,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct TicketChatDto {
+    pub session_id: String,
+    pub requester: String,
+    pub issue_ref: String,
+}
+
 /// Public link DTO.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
@@ -588,6 +612,43 @@ pub async fn ticket_read(
     Ok(TicketDto::from_issue(issue, carnet))
 }
 
+#[tauri::command]
+pub async fn open_ticket_chat(
+    request: OpenTicketChatRequestDto,
+    state: State<'_, AppState>,
+) -> Result<TicketChatDto, ErrorDto> {
+    let project = resolve_project(&state, &request.project_id).await?;
+    let output = state
+        .open_ticket_assistant
+        .execute(OpenTicketAssistantInput {
+            project,
+            issue_ref: parse_ref_dto(&request.issue_ref)?,
+            profile_id: parse_profile_id_dto(&request.profile_id)?,
+        })
+        .await
+        .map_err(ErrorDto::from)?;
+    Ok(TicketChatDto {
+        session_id: output.session_id.to_string(),
+        requester: output.requester,
+        issue_ref: output.issue_ref.to_string(),
+    })
+}
+
+#[tauri::command]
+pub async fn close_ticket_chat(
+    request: CloseTicketChatRequestDto,
+    state: State<'_, AppState>,
+) -> Result<(), ErrorDto> {
+    let _project = resolve_project(&state, &request.project_id).await?;
+    state
+        .close_ticket_assistant
+        .execute(CloseTicketAssistantInput {
+            issue_ref: parse_ref_dto(&request.issue_ref)?,
+        })
+        .await
+        .map_err(ErrorDto::from)
+}
+
 #[tauri::command]
 pub async fn ticket_list(
     request: TicketListRequestDto,
@@ -1234,6 +1295,12 @@ fn parse_agent_id_dto(raw: &str) -> Result<AgentId, ErrorDto> {
         .map_err(|e| ErrorDto::invalid(format!("invalid agent id: {e}")))
 }
 
+fn parse_profile_id_dto(raw: &str) -> Result<ProfileId, ErrorDto> {
+    Uuid::parse_str(raw)
+        .map(ProfileId::from_uuid)
+        .map_err(|e| ErrorDto::invalid(format!("invalid profile id: {e}")))
+}
+
 fn parse_sprint_id_dto(raw: &str) -> Result<SprintId, ErrorDto> {
     Uuid::parse_str(raw)
         .map(SprintId::from_uuid)