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/domain/src/events.rs

@@ -2,10 +2,13 @@
 //! presentation layer (ARCHITECTURE §3.2).
 
 use crate::conversation::ConversationParty;
-use crate::ids::{AgentId, IssueId, ProfileId, ProjectId, SessionId, SkillId, TaskId, TemplateId};
+use crate::ids::{
+    AgentId, IssueId, ProfileId, ProjectId, SessionId, SkillId, SprintId, TaskId, TemplateId,
+};
 use crate::issue::{IssueLinkKind, IssuePriority, IssueRef, IssueStatus, IssueVersion};
 use crate::mailbox::TicketId;
 use crate::memory::MemorySlug;
+use crate::sprint::{SprintOrder, SprintVersion};
 use crate::template::TemplateVersion;
 
 /// Which entry door a processed orchestration request arrived through.
@@ -367,6 +370,47 @@ pub enum DomainEvent {
         /// New optimistic version.
         version: IssueVersion,
     },
+    /// A sprint was created.
+    SprintCreated {
+        /// Stable sprint id.
+        sprint_id: SprintId,
+        /// Reorderable sprint order.
+        order: SprintOrder,
+    },
+    /// A sprint was renamed.
+    SprintRenamed {
+        /// Stable sprint id.
+        sprint_id: SprintId,
+        /// New sprint name.
+        name: String,
+        /// New optimistic version.
+        version: SprintVersion,
+    },
+    /// Sprint orders changed.
+    SprintReordered {
+        /// Stable sprint id.
+        sprint_id: SprintId,
+        /// New sprint order.
+        order: SprintOrder,
+        /// New optimistic version.
+        version: SprintVersion,
+    },
+    /// A sprint was deleted.
+    SprintDeleted {
+        /// Stable sprint id.
+        sprint_id: SprintId,
+    },
+    /// An issue was moved into, out of, or between sprints.
+    IssueSprintChanged {
+        /// Human-friendly issue reference.
+        issue_ref: IssueRef,
+        /// Previous sprint.
+        from: Option<SprintId>,
+        /// New sprint.
+        to: Option<SprintId>,
+        /// New optimistic version.
+        version: IssueVersion,
+    },
     /// A project's memory grew past the recall budget while no embedder is
     /// configured (strategy `none`): the first moment a semantic embedder would
     /// help (ARCHITECTURE §14.5.5, LOT C3). Published **at most once per session per