feat(agent): backend hot-swap profil (A0+A1) + inventaire reprise session (B1) — L15

Cadrage Architecture §15 (figé) : « agent = entité à session persistante ».

- A0 (domaine) : Agent::with_profile, LayoutTree::leaf, event AgentProfileChanged
  (+ DTO miroir DomainEventDto camelCase).
- A1 (application) : use case ChangeAgentProfile — no-op si profil identique,
  mutation manifeste, nettoyage conversation_id/agent_was_running sur layouts
  persistés, swap à chaud (kill PTY + relance même cellule via composition de
  LaunchAgent), event AgentProfileChanged. Décision : repartir à neuf (on garde
  .md + mémoire, on jette l'historique de conversation).
- B1 (application) : use case ListResumableAgents (lecture seule) — inventaire des
  cellules was_running||conversation_id, resume_supported selon profil, best-effort.

Aucun nouveau port/adapter (composition de l'existant). Hexagonal strict.
Tests : domaine 11 + app-tauri dto + ChangeAgentProfile 9 + ListResumableAgents 8,
suite application complète verte (0 régression).

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

crates/app-tauri/src/events.rs

@@ -47,6 +47,14 @@ pub enum DomainEventDto {
         /// Exit code.
         code: i32,
     },
+    /// An agent's runtime profile was changed (hot-swap of the AI engine).
+    #[serde(rename_all = "camelCase")]
+    AgentProfileChanged {
+        /// Agent id.
+        agent_id: String,
+        /// The new runtime profile id.
+        profile_id: String,
+    },
     /// A template was updated.
     #[serde(rename_all = "camelCase")]
     TemplateUpdated {
@@ -171,6 +179,13 @@ impl From<&DomainEvent> for DomainEventDto {
                 agent_id: agent_id.to_string(),
                 code: *code,
             },
+            DomainEvent::AgentProfileChanged {
+                agent_id,
+                profile_id,
+            } => Self::AgentProfileChanged {
+                agent_id: agent_id.to_string(),
+                profile_id: profile_id.to_string(),
+            },
             DomainEvent::TemplateUpdated {
                 template_id,
                 version,