fix(gdgxk): 打通登录全链路（图形验证码 OCR + 正确换票入口）

- 登录要过 4 位图形验证码：readCaptcha 返回 data:image/png;base64，用 ddddocr 识别，
  失败按登录页 #errorText 判断原因并最多重试 5 次
- 换票入口纠正：票按 ITLMS-xxx||ticketId 两段 GET /nts/loginToStoreByAccount，
  之前直接带 ?ticket= 访问 courseRegister 是无效的
- requirements / pyproject 增加 ddddocr；文档同步实测结论

src/study_tool/platforms/gdgxk.py

@@ -62,31 +62,67 @@ def dump_cookies(s):
 
 
 def _sso(s):
-    """jsglpt 会话换 ITLMS 票，再把票交给 jsxx 换学习会话。"""
+    """jsglpt 会话换 ITLMS 票，票按 `ITLMS-xxx||ticketId` 两段交给 jsxx。
+
+    交接入口来自 jsglpt 首页那个隐藏表单：
+    `GET https://jsxx.gds.edu.cn/nts/loginToStoreByAccount?ticket=&ticketId=`
+    """
     r = s.post(G + "/teacher/ssoItlmsGxkTicket.action?verificaCode=true&page=", timeout=30)
     ticket = (r.text or "").strip()
-    if not ticket.startswith("ITLMS-"):
+    if not ticket.startswith("ITLMS-") or "||" not in ticket:
         raise _expired("取 ITLMS 票失败：%s" % (ticket[:80] or "空响应"))
-    q = s.get(X + "/uc/store/courseRegister?ticket=" + requests.utils.quote(ticket), timeout=30)
-    if "showCourse" not in q.text and "我的课程" not in q.text:
-        raise _expired("带票进学习平台失败，可能票已失效")
+    t, tid = ticket.split("||", 1)
+    q = s.get(X + "/nts/loginToStoreByAccount", params={"ticket": t, "ticketId": tid}, timeout=30)
+    if "logout" not in q.text and "我的课程" not in q.text:
+        raise _expired("带票进学习平台失败，票可能已失效")
     return s
 
 
+_OCR = None
+
+
+def _ocr():
+    """4 位图形验证码：ddddocr 离线识别。"""
+    global _OCR
+    if _OCR is None:
+        try:
+            import ddddocr
+        except Exception as e:
+            raise RuntimeError("登录要过图形验证码，需要先装 ddddocr（pip install ddddocr）：%s" % e)
+        _OCR = ddddocr.DdddOcr(show_ad=False)
+    return _OCR
+
+
+def _captcha(s):
+    raw = s.get(G + "/login/readCaptcha.action?d=%.6f" % time.time(), timeout=30).text
+    return base64.b64decode(raw.strip().strip('"').split(",", 1)[-1])
+
+
+def _login_error(s):
+    html = s.get(G + "/login.jsp", timeout=30).text
+    m = re.search(r'id="errorText"[^>]*>([^<]*)<', html)
+    return (m.group(1).strip() if m else "")
+
+
 def login(username, password):
     s = new_session()
     s.get(G + "/login.jsp", timeout=30)
-    data = {
-        "loginUser.userName": _b64(username),
-        "loginUser.loginType": "normal",
-        "loginUser.password": _b64(password),
-        "captcha": "",
-    }
-    r = s.post(G + "/loginIn.do", data=data, allow_redirects=False, timeout=30)
-    if r.status_code != 302 or "/default.jsp" not in (r.headers.get("location") or ""):
-        raise RuntimeError("登录失败：账号或密码不对，或平台要求图形验证码（HTTP %s）" % r.status_code)
-    _sso(s)
-    return s, profile(s) or username
+    err = ""
+    for _ in range(5):
+        data = {
+            "loginUser.userName": _b64(username),
+            "loginUser.loginType": "normal",
+            "loginUser.password": _b64(password),
+            "captcha": _ocr().classification(_captcha(s)),
+        }
+        r = s.post(G + "/loginIn.do", data=data, allow_redirects=False, timeout=30)
+        if r.status_code == 302 and "/default.jsp" in (r.headers.get("location") or ""):
+            _sso(s)
+            return s, profile(s) or username
+        err = _login_error(s)
+        if "验证码" not in err:      # 不是验证码的问题，重试没意义
+            break
+    raise RuntimeError("登录失败：%s" % (err or "账号或密码不对"))
 
 
 def renew_session(s):