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/backend/src/dto.rs

@@ -1967,20 +1967,58 @@ pub fn parse_profile_id(raw: &str) -> Result<ProfileId, ErrorDto> {
 // ---------------------------------------------------------------------------
 
 use application::{
-    ChangeAgentProfileOutput, CreateAgentOutput, InspectConversationOutput, LaunchAgentOutput,
-    ListAgentsOutput, ReadAgentContextOutput, ReadMcpToolPermissionsOutput,
+    AgentCapability, ChangeAgentProfileOutput, CreateAgentOutput, InspectConversationOutput,
+    LaunchAgentOutput, ListAgentsOutput, ReadAgentContextOutput, ReadMcpToolPermissionsOutput,
 };
 use domain::{
     Agent, AgentMcpToolPolicyOverride, EffectivePermissions, McpToolPolicy, PermissionSet,
-    ProjectPermissions, TerminalSession,
+    ProjectPermissions, SkillKind, TerminalSession,
 };
 
-/// An agent crossing the wire. [`Agent`] already serialises camelCase
-/// (`id`, `name`, `contextPath`, `profileId`, `origin` tagged, `synchronized`),
-/// so we embed it directly — the TS mirror matches this shape.
+/// One discoverable capability carried by an agent.
 #[derive(Debug, Clone, Serialize)]
-#[serde(transparent)]
-pub struct AgentDto(pub Agent);
+#[serde(rename_all = "camelCase")]
+pub struct AgentCapabilityDto {
+    /// Capability display name.
+    pub name: String,
+    /// One-line affordance description.
+    pub description: String,
+    /// Capability nature.
+    pub kind: SkillKind,
+}
+
+impl From<AgentCapability> for AgentCapabilityDto {
+    fn from(value: AgentCapability) -> Self {
+        Self {
+            name: value.name,
+            description: value.description,
+            kind: value.kind,
+        }
+    }
+}
+
+/// An agent crossing the wire. The raw [`Agent`] shape is flattened so existing
+/// fields, including `skills`, remain compatible; `capabilities` is additive.
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct AgentDto {
+    /// Raw agent manifest shape.
+    #[serde(flatten)]
+    pub agent: Agent,
+    /// Resolved discoverable capabilities.
+    pub capabilities: Vec<AgentCapabilityDto>,
+}
+
+impl AgentDto {
+    /// Builds a DTO without resolved capabilities.
+    #[must_use]
+    pub fn from_agent(agent: Agent) -> Self {
+        Self {
+            agent,
+            capabilities: Vec::new(),
+        }
+    }
+}
 
 /// A list of agents (camelCase array on the wire).
 #[derive(Debug, Clone, Serialize)]
@@ -1989,13 +2027,25 @@ pub struct AgentListDto(pub Vec<AgentDto>);
 
 impl From<ListAgentsOutput> for AgentListDto {
     fn from(out: ListAgentsOutput) -> Self {
-        Self(out.agents.into_iter().map(AgentDto).collect())
+        Self(
+            out.discovery_entries()
+                .into_iter()
+                .map(|entry| AgentDto {
+                    agent: entry.agent,
+                    capabilities: entry
+                        .capabilities
+                        .into_iter()
+                        .map(AgentCapabilityDto::from)
+                        .collect(),
+                })
+                .collect(),
+        )
     }
 }
 
 impl From<CreateAgentOutput> for AgentDto {
     fn from(out: CreateAgentOutput) -> Self {
-        Self(out.agent)
+        Self::from_agent(out.agent)
     }
 }
 
@@ -2326,7 +2376,7 @@ pub struct ChangeAgentProfileDto {
 impl From<ChangeAgentProfileOutput> for ChangeAgentProfileDto {
     fn from(out: ChangeAgentProfileOutput) -> Self {
         Self {
-            agent: AgentDto(out.agent),
+            agent: AgentDto::from_agent(out.agent),
             relaunched_session: out.relaunched.map(TerminalSessionDto::from),
         }
     }