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/infrastructure/src/store/skill.rs

@@ -35,7 +35,7 @@ use domain::ids::SkillId;
 use domain::markdown::MarkdownDoc;
 use domain::ports::{FileSystem, RemotePath, SkillStore, StoreError};
 use domain::project::ProjectPath;
-use domain::skill::{Skill, SkillScope};
+use domain::skill::{Skill, SkillKind, SkillScope};
 
 /// Directory (under app-data) holding the global skills store.
 const GLOBAL_SKILLS_DIR: &str = "skills";
@@ -63,6 +63,9 @@ struct IndexEntry {
     /// field existed deserialise with `None` instead of failing.
     #[serde(default)]
     description: Option<String>,
+    /// Skill nature. Defaults to workflow for legacy index rows.
+    #[serde(default)]
+    kind: SkillKind,
     content_hash: String,
 }
 
@@ -195,6 +198,7 @@ impl FsSkillStore {
             scope,
         )
         .map(|skill| skill.with_description(entry.description.clone()))
+        .map(|skill| skill.with_kind(entry.kind))
         .map_err(|e| StoreError::Serialization(e.to_string()))
     }
 }
@@ -246,6 +250,7 @@ impl SkillStore for FsSkillStore {
             id: skill.id,
             name: skill.name.clone(),
             description: skill.description.clone(),
+            kind: skill.kind,
             content_hash: content_hash(&skill.content_md),
         };
         if let Some(slot) = index.skills.iter_mut().find(|e| e.id == skill.id) {
@@ -340,9 +345,9 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn legacy_index_without_description_loads_with_none() {
-        // A legacy `index.json` written before the `description` field existed must
-        // deserialise (thanks to `#[serde(default)]`) and load with `description: None`.
+    async fn legacy_index_without_description_loads_with_defaults() {
+        // A legacy `index.json` written before the `description`/`kind` fields
+        // existed must deserialise through additive defaults.
         let fs = MemFs::arc();
         let id = uuid::Uuid::from_u128(42);
         let legacy_index = format!(
@@ -367,14 +372,16 @@ mod tests {
         assert_eq!(listed.len(), 1);
         assert_eq!(listed[0].name, "legacy");
         assert_eq!(listed[0].description, None);
+        assert_eq!(listed[0].kind, SkillKind::Workflow);
         assert_eq!(listed[0].content_md.as_str(), "# legacy body");
     }
 
     #[tokio::test]
-    async fn save_then_load_round_trips_description() {
+    async fn save_then_load_round_trips_description_and_kind() {
         let store = FsSkillStore::new(MemFs::arc(), "/app");
         let s = skill(1, "refactor", "# Refactor\n\nbody")
-            .with_description(Some("Refactors code".to_owned()));
+            .with_description(Some("Refactors code".to_owned()))
+            .with_kind(SkillKind::Reference);
 
         store.save(&s, &root()).await.unwrap();
 
@@ -386,6 +393,7 @@ mod tests {
         let listed = store.list(SkillScope::Global, &root()).await.unwrap();
         assert_eq!(listed.len(), 1);
         assert_eq!(listed[0].description.as_deref(), Some("Refactors code"));
+        assert_eq!(listed[0].kind, SkillKind::Reference);
     }
 
     #[tokio::test]