feat(skills): capacités agent découvrables via idea_list_agents

Ajoute SkillKind (Workflow/Reference) sur Skill, extrait le use case
ResolveAgentCapabilities à partir des SkillRef assignés, et enrichit
idea_list_agents d'un champ additif capabilities (name, description,
kind) — remplace l'exposition de SkillRef opaques par un inventaire de
capacités interrogeable, source commune avec le bloc « Skills
disponibles » injecté au lancement (#119).

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

crates/application/tests/agent_lifecycle.rs

@@ -827,6 +827,43 @@ async fn list_reconstructs_agents_from_manifest() {
     assert_eq!(out.agents, vec![a]);
 }
 
+#[tokio::test]
+async fn list_resolves_agent_capabilities_additively() {
+    let mut a = scratch_agent(aid(1), "Backend", "agents/backend.md", pid(9));
+    let skill_id = SkillId::from_uuid(uuid::Uuid::from_u128(77));
+    a.assign_skill(domain::SkillRef::new(skill_id, domain::SkillScope::Global));
+    let contexts = FakeContexts::with_agent(&a, "ctx");
+    let skills = FakeSkills::with(vec![Skill::new(
+        skill_id,
+        "review",
+        MarkdownDoc::new("# Review workflow\n\nbody"),
+        domain::SkillScope::Global,
+    )
+    .unwrap()
+    .with_description(Some("Reviews changes".to_owned()))
+    .with_kind(domain::SkillKind::Reference)]);
+    let resolver = Arc::new(application::ResolveAgentCapabilities::new(Arc::new(skills)));
+    let list = ListAgents::with_capabilities(Arc::new(contexts), resolver);
+
+    let out = list
+        .execute(ListAgentsInput { project: project() })
+        .await
+        .unwrap();
+
+    assert_eq!(out.agents, vec![a.clone()]);
+    let entries = out.discovery_entries();
+    assert_eq!(entries.len(), 1);
+    assert_eq!(entries[0].agent.id, a.id);
+    assert_eq!(entries[0].agent.skills.len(), 1);
+    assert_eq!(entries[0].capabilities.len(), 1);
+    assert_eq!(entries[0].capabilities[0].name, "review");
+    assert_eq!(entries[0].capabilities[0].description, "Reviews changes");
+    assert_eq!(
+        entries[0].capabilities[0].kind,
+        domain::SkillKind::Reference
+    );
+}
+
 #[tokio::test]
 async fn read_then_update_context_roundtrips() {
     let a = scratch_agent(aid(1), "Backend", "agents/backend.md", pid(9));