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/issues.rs

@@ -16,7 +16,7 @@ use tokio::io::AsyncWriteExt;
 use domain::{
     AgentIssueRef, Issue, IssueActor, IssueCarnet, IssueId, IssueIndexEntry, IssueLink,
     IssueListFilter, IssueNumber, IssueNumberAllocator, IssuePriority, IssueRef, IssueStatus,
-    IssueStore, IssueStoreError, IssueVersion, MarkdownDoc, ProjectPath,
+    IssueStore, IssueStoreError, IssueVersion, MarkdownDoc, ProjectPath, SprintId,
 };
 
 const IDEAI_DIR: &str = ".ideai";
@@ -211,6 +211,12 @@ fn filter_matches(row: &IssueIndexEntry, filter: &IssueListFilter) -> bool {
             return false;
         }
     }
+    if filter
+        .sprint
+        .is_some_and(|sprint| row.sprint != Some(sprint))
+    {
+        return false;
+    }
     if let Some(text) = filter
         .text
         .as_ref()
@@ -423,6 +429,7 @@ number: {}\n\
 title: {}\n\
 status: {}\n\
 priority: {}\n\
+sprint: {}\n\
 links: {}\n\
 agentRefs: {}\n\
 createdBy: {}\n\
@@ -436,6 +443,7 @@ version: {}\n\
         json_string(&issue.title),
         json_value(&issue.status),
         json_value(&issue.priority),
+        json_value(&issue.sprint),
         json_value(&issue.links),
         json_value(&issue.agent_refs),
         json_value(&issue.created_by),
@@ -475,6 +483,7 @@ fn parse_issue_doc(text: &str) -> Result<Issue, IssueStoreError> {
     let title: String = parse_json_field(&map, "title")?;
     let status: IssueStatus = parse_json_field(&map, "status")?;
     let priority: IssuePriority = parse_json_field(&map, "priority")?;
+    let sprint: Option<SprintId> = parse_optional_json_field(&map, "sprint")?.unwrap_or(None);
     let links: Vec<IssueLink> = parse_json_field(&map, "links")?;
     let agent_refs: Vec<AgentIssueRef> = parse_json_field(&map, "agentRefs")?;
     let created_by: IssueActor = parse_json_field(&map, "createdBy")?;
@@ -490,6 +499,7 @@ fn parse_issue_doc(text: &str) -> Result<Issue, IssueStoreError> {
         description: MarkdownDoc::new(body),
         status,
         priority,
+        sprint,
         carnet: MarkdownDoc::default(),
         links,
         agent_refs,
@@ -567,6 +577,18 @@ fn parse_json_field<T: serde::de::DeserializeOwned>(
     serde_json::from_str(value).map_err(|err| IssueStoreError::Invalid(err.to_string()))
 }
 
+fn parse_optional_json_field<T: serde::de::DeserializeOwned>(
+    map: &BTreeMap<String, String>,
+    key: &str,
+) -> Result<Option<T>, IssueStoreError> {
+    let Some(value) = map.get(key) else {
+        return Ok(None);
+    };
+    serde_json::from_str(value)
+        .map(Some)
+        .map_err(|err| IssueStoreError::Invalid(err.to_string()))
+}
+
 fn json_value<T: Serialize>(value: &T) -> String {
     serde_json::to_string(value).expect("serializing issue frontmatter cannot fail")
 }