refactor(scenario): remove validateCode — assertions live in execCode

- drop validateCode column, DTOs, service mappings, and scheduler branch
- remove parseValidateResult helper and ValidateResult interface
- inject playwright expect into code executor for direct use in execCode
- strip validateCode from MCP tool schemas, client types, and UI forms

server/test/scenario.controller.spec.ts

@@ -477,7 +477,6 @@ describe("ScenarioController", () => {
         order: 1,
         sessionName: "s",
         execCode: "return 1;",
-        validateCode: "return true;",
       });
 
       const res = await request(app.getHttpServer())
@@ -536,25 +535,6 @@ describe("ScenarioController", () => {
       expect(step).not.toHaveProperty("updatedAt");
     });
 
-    it("exports null validateCode as null", async () => {
-      const sc = await createScenario("export-null-validate");
-      await createStep(sc.id, {
-        order: 0,
-        sessionName: "s",
-        execCode: "return 1;",
-      });
-
-      const res = await request(app.getHttpServer())
-        .get(`/scenarios/${sc.id}/export`)
-        .expect(200);
-
-      const exported = yamlParse(res.text) as {
-        steps: Array<{ validateCode: string | null }>;
-      };
-
-      expect(exported.steps[0].validateCode).toBeNull();
-    });
-
     it("returns 404 for unknown scenario", async () => {
       await request(app.getHttpServer())
         .get("/scenarios/00000000-0000-0000-0000-000000000001/export")
@@ -572,17 +552,14 @@ describe("ScenarioController", () => {
           {
             sessionName: "s",
             execCode: '{"keyId":"k","environmentName":"e"}',
-            validateCode: null,
           },
           {
             sessionName: "s",
             execCode: "return 1;",
-            validateCode: "return true;",
           },
           {
             sessionName: "s",
             execCode: '{"keyId":"k"}',
-            validateCode: null,
           },
         ],
       };
@@ -622,7 +599,6 @@ describe("ScenarioController", () => {
         order: 0,
         sessionName: "rs",
         execCode: "return 42;",
-        validateCode: "return true;",
       });
 
       const exportRes = await request(app.getHttpServer())
@@ -630,7 +606,7 @@ describe("ScenarioController", () => {
         .expect(200);
 
       const exported = yamlParse(exportRes.text) as {
-        steps: Array<{ execCode: string; validateCode: string | null }>;
+        steps: Array<{ execCode: string }>;
       };
 
       const importRes = await request(app.getHttpServer())
@@ -643,9 +619,6 @@ describe("ScenarioController", () => {
       expect(importRes.body.steps[0].execCode).toBe(
         exported.steps[0].execCode,
       );
-      expect(importRes.body.steps[0].validateCode).toBe(
-        exported.steps[0].validateCode,
-      );
     });
 
     it("imports with empty steps array", async () => {