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.js

@@ -0,0 +1,38 @@
+export function section(title) {
+  console.log(`\n=== ${title} ===`);
+}
+
+export function step(stepName, title) {
+  console.log(`\n[${stepName}] ${title}`);
+}
+
+export function line(message) {
+  console.log(`  - ${message}`);
+}
+
+/** 階段輸入：這個階段吃進什麼。 */
+export function input(message) {
+  console.log(`  ← 輸入：${message}`);
+}
+
+/** 階段輸出：這個階段產出什麼。 */
+export function output(message) {
+  console.log(`  → 輸出：${message}`);
+}
+
+/** 檢查／把關結果：明確標示成功或失敗。 */
+export function result(passed, message) {
+  console.log(`  ${passed ? '✅ 成功' : '❌ 失敗'}：${message}`);
+}
+
+export function ok(message) {
+  console.log(`  ✓ ${message}`);
+}
+
+export function warn(message) {
+  console.warn(`  ! ${message}`);
+}
+
+export function error(message) {
+  console.error(`  x ${message}`);
+}