refactor: replace requireEnv/optionalEnv with env(name, fallback)

Bundles must run without env vars — env vars are overrides, not requirements.
Single function: env(name, fallback) always returns string with a default.

- Removed requireEnv and optionalEnv
- Updated bundle entries, tests, and skill docs

小橘 🍊

packages/workflow-util/__tests__/env.test.ts

@@ -1,44 +1,20 @@
-import { describe, expect, test } from "bun:test";
-import { optionalEnv, requireEnv } from "../src/env.js";
+import { describe, expect, it } from "bun:test";
+import { env } from "../src/env.js";
 
-describe("requireEnv", () => {
-  test("returns value when set", () => {
-    process.env.TEST_REQ = "hello";
-    expect(requireEnv("TEST_REQ", "missing")).toBe("hello");
-    delete process.env.TEST_REQ;
+describe("env", () => {
+  it("returns env value when set", () => {
+    process.env.TEST_ENV_SET = "hello";
+    expect(env("TEST_ENV_SET", "default")).toBe("hello");
+    delete process.env.TEST_ENV_SET;
   });
 
-  test("throws with message when missing", () => {
-    expect(() => requireEnv("TEST_MISSING_XYZ", "need this")).toThrow("need this");
+  it("returns fallback when missing", () => {
+    expect(env("TEST_ENV_MISSING_XYZ", "fallback")).toBe("fallback");
   });
 
-  test("throws when empty string", () => {
-    process.env.TEST_EMPTY = "";
-    expect(() => requireEnv("TEST_EMPTY", "cannot be empty")).toThrow("cannot be empty");
-    delete process.env.TEST_EMPTY;
-  });
-});
-
-describe("optionalEnv", () => {
-  test("returns value when set", () => {
-    process.env.TEST_OPT = "world";
-    expect(optionalEnv("TEST_OPT")).toBe("world");
-    expect(optionalEnv("TEST_OPT", "default")).toBe("world");
-    delete process.env.TEST_OPT;
-  });
-
-  test("returns null when missing and no fallback", () => {
-    expect(optionalEnv("TEST_MISSING_ABC")).toBeNull();
-  });
-
-  test("returns fallback when missing", () => {
-    expect(optionalEnv("TEST_MISSING_ABC", "fallback")).toBe("fallback");
-  });
-
-  test("returns fallback when empty string", () => {
-    process.env.TEST_EMPTY2 = "";
-    expect(optionalEnv("TEST_EMPTY2", "fb")).toBe("fb");
-    expect(optionalEnv("TEST_EMPTY2")).toBeNull();
-    delete process.env.TEST_EMPTY2;
+  it("returns fallback when empty", () => {
+    process.env.TEST_ENV_EMPTY = "";
+    expect(env("TEST_ENV_EMPTY", "fb")).toBe("fb");
+    delete process.env.TEST_ENV_EMPTY;
   });
 });