feat(HAI-113): add structured logger and replace console calls

- Create logger module with log levels and structured output (packages/engine/src/logger.ts)
- Replace console.log/warn/error calls with structured logger across engine modules
- Export logger from engine package index
- Add comprehensive tests for logger functionality
- Clean up CI/release workflows and update docs

packages/engine/src/logger.test.ts

@@ -0,0 +1,75 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { createLogger, schedulerLog, executorLog, triageLog, mergerLog, worktreePoolLog, reviewerLog } from "./logger.js";
+
+describe("createLogger", () => {
+  let logSpy: ReturnType<typeof vi.spyOn>;
+  let warnSpy: ReturnType<typeof vi.spyOn>;
+  let errorSpy: ReturnType<typeof vi.spyOn>;
+
+  beforeEach(() => {
+    logSpy = vi.spyOn(console, "log").mockImplementation(() => {});
+    warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    errorSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+  });
+
+  afterEach(() => {
+    logSpy.mockRestore();
+    warnSpy.mockRestore();
+    errorSpy.mockRestore();
+  });
+
+  it("formats log output as [prefix] message", () => {
+    const logger = createLogger("test");
+    logger.log("hello world");
+    expect(logSpy).toHaveBeenCalledWith("[test] hello world");
+  });
+
+  it("formats warn output as [prefix] message", () => {
+    const logger = createLogger("test");
+    logger.warn("something happened");
+    expect(warnSpy).toHaveBeenCalledWith("[test] something happened");
+  });
+
+  it("formats error output as [prefix] message", () => {
+    const logger = createLogger("test");
+    logger.error("failure");
+    expect(errorSpy).toHaveBeenCalledWith("[test] failure");
+  });
+
+  it("passes extra arguments through", () => {
+    const logger = createLogger("test");
+    const err = new Error("boom");
+    logger.error("failed:", err);
+    expect(errorSpy).toHaveBeenCalledWith("[test] failed:", err);
+  });
+
+  it("delegates log to console.log, warn to console.warn, error to console.error", () => {
+    const logger = createLogger("x");
+    logger.log("a");
+    logger.warn("b");
+    logger.error("c");
+    expect(logSpy).toHaveBeenCalledTimes(1);
+    expect(warnSpy).toHaveBeenCalledTimes(1);
+    expect(errorSpy).toHaveBeenCalledTimes(1);
+  });
+
+  it("pre-built instances use correct prefixes", () => {
+    schedulerLog.log("tick");
+    expect(logSpy).toHaveBeenCalledWith("[scheduler] tick");
+
+    executorLog.log("run");
+    expect(logSpy).toHaveBeenCalledWith("[executor] run");
+
+    triageLog.log("spec");
+    expect(logSpy).toHaveBeenCalledWith("[triage] spec");
+
+    mergerLog.log("merge");
+    expect(logSpy).toHaveBeenCalledWith("[merger] merge");
+
+    worktreePoolLog.log("prune");
+    expect(logSpy).toHaveBeenCalledWith("[worktree-pool] prune");
+
+    reviewerLog.log("review");
+    expect(logSpy).toHaveBeenCalledWith("[reviewer] review");
+  });
+});