feat: add agent-mock package for deterministic E2E testing (#33)

New package @united-workforce/agent-mock (uwf-mock CLI):
- Reads pre-scripted outputs from a YAML mock data file (--mock-data)
- Counts existing CAS chain steps to determine step index
- Validates expected role matches actual moderator routing
- Stores minimal detail node in CAS for valid step refs
- Zero LLM, instant execution, 100% deterministic

Usage in config.yaml:
  agents:
    mock:
      command: uwf-mock
      args: ["--mock-data", "./fixtures/scenario.yaml"]

Refs #33

packages/agent-mock/__tests__/mock-agent.test.ts

@@ -0,0 +1,48 @@
+import { readFile } from "node:fs/promises";
+import { join } from "node:path";
+import { describe, expect, test } from "vitest";
+
+import { parseScenario, selectMockStep } from "../src/mock-agent.js";
+
+const FIXTURE = join(__dirname, "fixtures", "simple-scenario.yaml");
+
+describe("parseScenario", () => {
+  test("parses the 2-step fixture in order", async () => {
+    const scenario = parseScenario(await readFile(FIXTURE, "utf8"));
+    expect(scenario.steps).toHaveLength(2);
+    expect(scenario.steps[0].role).toBe("planner");
+    expect(scenario.steps[1].role).toBe("developer");
+    expect(scenario.steps[0].output).toContain("$status: ready");
+    expect(scenario.steps[1].output).toContain("branch: fix/1-test");
+  });
+
+  test("rejects documents without a steps array", () => {
+    expect(() => parseScenario("foo: bar")).toThrow(/steps/);
+  });
+
+  test("rejects steps missing role or output", () => {
+    expect(() => parseScenario("steps:\n  - role: planner")).toThrow(/role.*output/);
+  });
+});
+
+describe("selectMockStep", () => {
+  const scenario = {
+    steps: [
+      { role: "planner", output: "plan-output" },
+      { role: "developer", output: "dev-output" },
+    ],
+  };
+
+  test("step index counts existing steps to pick the current step", () => {
+    expect(selectMockStep(scenario, 0, "planner").output).toBe("plan-output");
+    expect(selectMockStep(scenario, 1, "developer").output).toBe("dev-output");
+  });
+
+  test("throws when the moderator routes to an unexpected role", () => {
+    expect(() => selectMockStep(scenario, 0, "developer")).toThrow(/expected role "planner"/);
+  });
+
+  test("throws when the step index runs past the scripted steps", () => {
+    expect(() => selectMockStep(scenario, 2, "planner")).toThrow(/no step at index 2/);
+  });
+});