feat: add role management and usage tracking modules

- Implemented role parsing and loading functionality in roles.js, allowing for structured role definitions with metadata.
- Added tests for role management to ensure correct parsing and loading of roles.
- Created usage.js to track API usage metrics, including token counts and rate limits.
- Developed tests for usage tracking to validate functionality and edge cases.
- Enhanced overall code structure and documentation for clarity and maintainability.

app/log.test.js

@@ -0,0 +1,78 @@
+import { describe, it, afterEach, mock } from 'node:test';
+import assert from 'node:assert/strict';
+import { section, step, line, input, output, result, ok, warn, error } from './log.js';
+
+afterEach(() => mock.restoreAll());
+
+describe('log helpers', () => {
+  it('formats section and step messages', () => {
+    const calls = [];
+    mock.method(console, 'log', (...args) => {
+      calls.push(args.join(' '));
+    });
+
+    section('Pipeline');
+    step('Step1', 'Start');
+
+    assert.deepEqual(calls, [
+      '\n=== Pipeline ===',
+      '\n[Step1] Start',
+    ]);
+  });
+
+  it('formats line and ok messages with console.log', () => {
+    const calls = [];
+    mock.method(console, 'log', (...args) => {
+      calls.push(args.join(' '));
+    });
+
+    line('hello');
+    ok('done');
+
+    assert.deepEqual(calls, [
+      '  - hello',
+      '  ✓ done',
+    ]);
+  });
+
+  it('formats input/output and pass/fail result messages', () => {
+    const calls = [];
+    mock.method(console, 'log', (...args) => {
+      calls.push(args.join(' '));
+    });
+
+    input('5 筆');
+    output('3 筆');
+    result(true, '通過');
+    result(false, '未通過');
+
+    assert.deepEqual(calls, [
+      '  ← 輸入：5 筆',
+      '  → 輸出：3 筆',
+      '  ✅ 成功：通過',
+      '  ❌ 失敗：未通過',
+    ]);
+  });
+
+  it('formats warn messages with console.warn', () => {
+    const calls = [];
+    mock.method(console, 'warn', (...args) => {
+      calls.push(args.join(' '));
+    });
+
+    warn('careful');
+
+    assert.deepEqual(calls, ['  ! careful']);
+  });
+
+  it('formats error messages with console.error', () => {
+    const calls = [];
+    mock.method(console, 'error', (...args) => {
+      calls.push(args.join(' '));
+    });
+
+    error('boom');
+
+    assert.deepEqual(calls, ['  x boom']);
+  });
+});