feat(sprints): modèle de sprints — domaine, use-cases, persistance et surfaces (backend)

Ticket #10 — introduction du modèle de sprints côté backend.

- Domaine : nouvel agrégat Sprint (sprint.rs), IDs, événements et invariants ;
  rattachement des issues à un sprint (issue.rs) et ports associés.
- Application : use-cases sprints (application/src/sprints) + erreurs dédiées.
- Infrastructure : store de sprints (infrastructure/src/sprints.rs), adaptation
  du store d'issues et exposition MCP via orchestrator/mcp/tickets.rs.
- app-tauri : commandes, state et events pour piloter les sprints depuis l'UI.

Tests domaine/application/infra/app-tauri verts (sprint_usecases, sprint_store,
issue_store, mcp_server).

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

crates/infrastructure/src/orchestrator/mcp/tickets.rs

@@ -39,7 +39,7 @@ impl TicketToolError {
 /// Provider injected by the composition root to execute public ticket tools.
 #[async_trait]
 pub trait TicketToolProvider: Send + Sync {
-    /// Executes one public `idea_ticket_*` tool for `project`.
+    /// Executes one public ticket/sprint planning tool for `project`.
     async fn handle_ticket_tool(
         &self,
         project: &Project,
@@ -64,6 +64,7 @@ pub fn is_ticket_tool(name: &str) -> bool {
             | "idea_ticket_update_carnet"
             | "idea_ticket_link"
             | "idea_ticket_unlink"
+            | "idea_sprint_list"
     )
 }
 
@@ -234,5 +235,14 @@ pub fn catalogue() -> Vec<ToolDef> {
                 "additionalProperties": false
             }),
         },
+        ToolDef {
+            name: "idea_sprint_list",
+            description: "List IdeA sprints in execution order. Read-only.",
+            input_schema: json!({
+                "type": "object",
+                "properties": {},
+                "additionalProperties": false
+            }),
+        },
     ]
 }