refactor: add new suggestion for filterDiff unit tests and update getPRDiff documentation for clarity

app/gitea.js

@@ -6,6 +6,10 @@ const httpsAgent = GITEA_SKIP_TLS_VERIFY ? new https.Agent({ rejectUnauthorized:
 const headers = () => ({ Authorization: `token ${GITEA_TOKEN}`, 'Content-Type': 'application/json' });
 const api = (path) => `${GITEA_SERVER_URL.replace(/\/$/, '')}/api/v1${path}`;
 
+/**
+ * 取得 PR 的原始 Git Diff 內容。
+ * 注意：回傳值未經路徑過濾，呼叫端須使用 filterDiff 排除敏感路徑（如 .gitea/）後再傳給 AI。
+ */
 export async function getPRDiff() {
   const resp = await axios.get(api(`/repos/${GITEA_REPOSITORY}/pulls/${PR_NUMBER}.diff`), { headers: headers(), timeout: 60000, httpsAgent });
   return resp.data;