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/ports.rs

@@ -32,7 +32,7 @@ use crate::background_task::{
     BackgroundTask, BackgroundTaskKind, BackgroundTaskResult, BackgroundTaskWakePolicy,
 };
 use crate::events::DomainEvent;
-use crate::ids::{AgentId, NodeId, ProjectId, ScheduleId, SessionId, TaskId};
+use crate::ids::{AgentId, NodeId, ProjectId, ScheduleId, SessionId, SprintId, TaskId};
 use crate::issue::{
     Issue, IssueCarnet, IssueIndexEntry, IssueListFilter, IssueNumber, IssueRef, IssueVersion,
 };
@@ -43,6 +43,7 @@ use crate::profile::{AgentProfile, EmbedderProfile};
 use crate::project::{Project, ProjectPath};
 use crate::remote::RemoteKind;
 use crate::skill::{Skill, SkillScope};
+use crate::sprint::{Sprint, SprintIndexEntry, SprintVersion};
 use crate::template::AgentTemplate;
 use crate::terminal::PtySize;
 
@@ -596,6 +597,28 @@ pub enum IssueStoreError {
     #[error("issue store failed: {0}")]
     Store(String),
 }
+
+/// Errors from the sprint store.
+#[derive(Debug, Clone, PartialEq, Eq, Error)]
+pub enum SprintStoreError {
+    /// The requested sprint does not exist.
+    #[error("sprint not found")]
+    NotFound,
+    /// Optimistic concurrency conflict.
+    #[error("sprint version conflict: expected {expected}, actual {actual}")]
+    VersionConflict {
+        /// Expected version.
+        expected: SprintVersion,
+        /// Actual persisted version.
+        actual: SprintVersion,
+    },
+    /// The sprint payload is invalid.
+    #[error("sprint invalid: {0}")]
+    Invalid(String),
+    /// Store I/O or serialization failed.
+    #[error("sprint store failed: {0}")]
+    Store(String),
+}
 // ---------------------------------------------------------------------------
 // Git port support types
 // ---------------------------------------------------------------------------
@@ -1507,6 +1530,50 @@ pub trait IssueStore: Send + Sync {
     ) -> Result<IssueCarnet, IssueStoreError>;
 }
 
+/// Persistence port for project-scoped sprints.
+#[async_trait]
+pub trait SprintStore: Send + Sync {
+    /// Creates a new sprint.
+    ///
+    /// # Errors
+    /// [`SprintStoreError`] when the sprint already exists or cannot be stored.
+    async fn create(&self, root: &ProjectPath, sprint: &Sprint) -> Result<(), SprintStoreError>;
+
+    /// Reads a sprint by stable id.
+    ///
+    /// # Errors
+    /// [`SprintStoreError::NotFound`] when absent.
+    async fn get(
+        &self,
+        root: &ProjectPath,
+        sprint_id: SprintId,
+    ) -> Result<Sprint, SprintStoreError>;
+
+    /// Lists sprint index entries.
+    ///
+    /// # Errors
+    /// [`SprintStoreError`] on persistence failure.
+    async fn list(&self, root: &ProjectPath) -> Result<Vec<SprintIndexEntry>, SprintStoreError>;
+
+    /// Replaces a sprint after checking its expected version.
+    ///
+    /// # Errors
+    /// [`SprintStoreError::VersionConflict`] on optimistic-concurrency conflict.
+    async fn update(
+        &self,
+        root: &ProjectPath,
+        sprint: &Sprint,
+        expected_version: SprintVersion,
+    ) -> Result<(), SprintStoreError>;
+
+    /// Deletes a sprint by id.
+    ///
+    /// # Errors
+    /// [`SprintStoreError::NotFound`] when absent.
+    async fn delete(&self, root: &ProjectPath, sprint_id: SprintId)
+        -> Result<(), SprintStoreError>;
+}
+
 /// Git operations for a project. Named `GitPort` to avoid clashing with the
 /// [`crate::git::GitRepository`] *entity* (state image).
 #[async_trait]