wip(tickets): backend createdBy (#5) + bulk status/priority/delete (#6)

Ajoute created_by sur IssueIndexEntry/TicketSummaryDto + filtre createdBy
(#5), et les use cases BulkUpdateIssueStatus/Priority + BulkDeleteIssues
avec les DTO/outils MCP idea_ticket_bulk_* associés (#6).

NON VERT : BulkDeleteIssues::execute référence BatchIssueResult::deleted(),
constructeur pas encore ajouté à BatchIssueResult (seuls ok/err existent) ->
`cargo check` échoue (E0599 dans application::issues::mod). Reste à
DevBackend avant toute QA/merge.

Branché sur feature/sdk-integration (dépend du commit #2 dans
orchestrator/mcp/server.rs et tools.rs) ; à rebaser sur develop une fois
feature/sdk-integration mergé.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/domain/tests/issue.rs

@@ -1,8 +1,9 @@
 use std::str::FromStr;
 
 use domain::{
-    AgentIssueRef, AgentIssueRole, Issue, IssueActor, IssueError, IssueId, IssueLink,
-    IssueLinkKind, IssueNumber, IssuePriority, IssueRef, IssueStatus, IssueVersion, MarkdownDoc,
+    AgentIssueRef, AgentIssueRole, Issue, IssueActor, IssueError, IssueId, IssueIndexEntry,
+    IssueLink, IssueLinkKind, IssueNumber, IssuePriority, IssueRef, IssueStatus, IssueVersion,
+    MarkdownDoc,
 };
 
 fn issue_number(n: u64) -> IssueNumber {
@@ -118,3 +119,26 @@ fn issue_mutation_increments_version_and_updates_actor_time() {
     assert_eq!(updated.updated_by, IssueActor::System);
     assert_eq!(updated.updated_at, 2_000);
 }
+
+#[test]
+fn issue_index_entry_reuses_created_by_source_of_truth() {
+    let agent_id = domain::AgentId::new_random();
+    let issue = Issue::new(
+        IssueId::new_random(),
+        issue_number(11),
+        "Agent-created",
+        MarkdownDoc::new("Description"),
+        IssueStatus::Open,
+        IssuePriority::Medium,
+        MarkdownDoc::default(),
+        Vec::new(),
+        Vec::new(),
+        IssueActor::Agent { agent_id },
+        1,
+    )
+    .unwrap();
+
+    let row = IssueIndexEntry::from(&issue);
+
+    assert_eq!(row.created_by, IssueActor::Agent { agent_id });
+}