feat(agent): UI hot-swap de profil (A2) — commande Tauri + sélecteur + dialog

- Tauri : commande change_agent_profile + ChangeAgentProfileRequestDto/Dto
  (camelCase, relaunchedSession omis si None), câblage state.rs par composition.
- Front : gateway changeAgentProfile (adapters Tauri+mock), sélecteur de profil
  par agent, dialog de confirmation FR (« Changer le moteur abandonne l'historique
  de conversation… »), refresh sur event agentProfileChanged.

Tests : app-tauri dto 5/5 ; vitest 314/314 (mapping, payload, dialog gating,
libellé FR, refresh). 0 régression.

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

frontend/src/adapters/agent.test.ts

@@ -69,4 +69,53 @@ describe("TauriAgentGateway invoke payloads", () => {
       request: { projectId: "proj-1", agentId: "agent-2", nodeId: "node-3" },
     });
   });
+
+  it("change_agent_profile wraps all five fields in the request DTO (camelCase)", async () => {
+    invoke.mockResolvedValueOnce({ agent: { id: "agent-2" } });
+    await new TauriAgentGateway().changeAgentProfile(
+      "proj-1",
+      "agent-2",
+      "prof-9",
+      30,
+      120,
+    );
+    expect(invoke).toHaveBeenCalledWith("change_agent_profile", {
+      request: {
+        projectId: "proj-1",
+        agentId: "agent-2",
+        profileId: "prof-9",
+        rows: 30,
+        cols: 120,
+      },
+    });
+  });
+
+  it("change_agent_profile returns the mutated agent and the relaunched session", async () => {
+    const response = {
+      agent: { id: "agent-2", profileId: "prof-9" },
+      relaunchedSession: { sessionId: "sess-7", cwd: "/p", rows: 30, cols: 120 },
+    };
+    invoke.mockResolvedValueOnce(response);
+    const out = await new TauriAgentGateway().changeAgentProfile(
+      "proj-1",
+      "agent-2",
+      "prof-9",
+      30,
+      120,
+    );
+    expect(out.agent.profileId).toBe("prof-9");
+    expect(out.relaunchedSession?.sessionId).toBe("sess-7");
+  });
+
+  it("change_agent_profile leaves relaunchedSession undefined when the backend omits it", async () => {
+    invoke.mockResolvedValueOnce({ agent: { id: "agent-2" } });
+    const out = await new TauriAgentGateway().changeAgentProfile(
+      "proj-1",
+      "agent-2",
+      "prof-9",
+      30,
+      120,
+    );
+    expect(out.relaunchedSession).toBeUndefined();
+  });
 });