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/src/mcp/mcp.service.ts

@@ -505,10 +505,6 @@ export class McpService {
             .string()
             .optional()
             .describe("Playwright JS code to execute (exec steps)"),
-          validateCode: z
-            .string()
-            .optional()
-            .describe("Validation JS code returning { success, description }"),
         },
       },
       async ({ scenarioId, ...dto }) => {
@@ -569,7 +565,6 @@ export class McpService {
             .describe("New step type"),
           title: z.string().optional().describe("New step title"),
           execCode: z.string().optional().describe("New exec code"),
-          validateCode: z.string().optional().describe("New validation code"),
         },
       },
       async ({ scenarioId, stepId, ...dto }) => {
@@ -785,11 +780,6 @@ export class McpService {
                   .nullable()
                   .optional()
                   .describe("Exec/sign code"),
-                validateCode: z
-                  .string()
-                  .nullable()
-                  .optional()
-                  .describe("Validation code"),
               }),
             )
             .describe("Ordered list of steps"),