refactor(calculate-version): 抽出 truncateString 並明確化 repository 驗證命名

- releases 將片段截斷邏輯抽為可重用、可獨立測試的 truncateString(text, limit) 並 export
- config 將 assertRepository 更名為 assertGiteaRepositoryFormat，凸顯其驗證 Gitea owner/repo 格式的領域語義

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/config.js

@@ -68,7 +68,7 @@ function isValidRepoSegment(part) {
 }
 
 // 驗證 repository 為 owner/repo 格式（恰兩段，且每段皆為合法區段）
-function assertRepository(name, value) {
+function assertGiteaRepositoryFormat(name, value) {
     const parts = value.split('/');
     const isRepoFormatValid = parts.length === 2 && parts.every(isValidRepoSegment);
     if (!isRepoFormatValid) {
@@ -91,7 +91,7 @@ function loadConfig(env = process.env) {
     const serverUrl = requireEnv('GITEA_SERVER_URL', env.GITEA_SERVER_URL);
     assertHttpUrl('GITEA_SERVER_URL', serverUrl);
     const repository = requireEnv('GITEA_REPOSITORY', env.GITEA_REPOSITORY);
-    assertRepository('GITEA_REPOSITORY', repository);
+    assertGiteaRepositoryFormat('GITEA_REPOSITORY', repository);
     const token = isUnset(env.GITEA_TOKEN) ? null : env.GITEA_TOKEN;
     const isBeta = normalizeBetaFlag(env.IS_BETA);