refactor: 移除注册验证码，删掉 pillow

验证码只剩注册一处调用方，一并去掉。

- UserRegisterAPI 的校验、UserRegisterSerializer 的 captcha 字段、
  发图的 captcha 路由
- utils/captcha/ 整个包删除，含 Menlo.ttc 和 timesbi.ttf 两个字体
- utils/shortcuts.py 的 img2base64()，唯一调用方是验证码视图
- 依赖删除 pillow（本地实测 PIL/ 5.9M + pillow.libs/ 14M）

注意：注册接口现在只有 SysOptions.allow_register 一个开关，没有限流，
throttling 目前只用在 SubmissionAPI 上。内网自用可以接受，站点若暴露到
公网需要补 IP 维度限流。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

utils/captcha/__init__.py

@@ -1,100 +0,0 @@
-"""
-Copyright 2013 TY<tianyu0915@gmail.com>
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-  http://www.apache.org/licenses/LICENSE-2.0
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-"""
-
-import os
-import random
-import time
-
-from PIL import Image, ImageDraw, ImageFont
-
-
-class Captcha(object):
-    def __init__(self, request):
-        """
-        初始化,设置各种属性
-        """
-        self.django_request = request
-        self.session_key = "_django_captcha_key"
-        self.captcha_expires_time = "_django_captcha_expires_time"
-
-        # 验证码图片尺寸
-        self.img_width = 90
-        self.img_height = 30
-
-    def _get_font_size(self, code):
-        """
-        将图片高度的80%作为字体大小
-        """
-        s1 = int(self.img_height * 0.8)
-        s2 = int(self.img_width / len(code))
-        return int(min((s1, s2)) + max((s1, s2)) * 0.05)
-
-    def _set_answer(self, answer):
-        """
-        设置答案和过期时间
-        """
-        self.django_request.session[self.session_key] = str(answer)
-        self.django_request.session[self.captcha_expires_time] = time.time() + 60
-
-    def _make_code(self):
-        """
-        生成随机数或随机字符串
-        """
-        string = random.sample("abcdefghkmnpqrstuvwxyzABCDEFGHGKMNOPQRSTUVWXYZ23456789", 4)
-        self._set_answer("".join(string))
-        return string
-
-    def get(self):
-        """
-        生成验证码图片,返回值为图片的bytes
-        """
-        background = (random.randrange(200, 255), random.randrange(200, 255), random.randrange(200, 255))
-        code_color = (random.randrange(0, 50), random.randrange(0, 50), random.randrange(0, 50), 255)
-
-        font_path = os.path.join(os.path.normpath(os.path.dirname(__file__)), "timesbi.ttf")
-
-        image = Image.new("RGB", (self.img_width, self.img_height), background)
-        code = self._make_code()
-        font_size = self._get_font_size(code)
-        draw = ImageDraw.Draw(image)
-
-        # x是第一个字母的x坐标
-        x = random.randrange(int(font_size * 0.3), int(font_size * 0.5))
-
-        for i in code:
-            # 字符y坐标
-            y = random.randrange(1, 7)
-            # 随机字符大小
-            font = ImageFont.truetype(font_path.replace("\\", "/"), font_size + random.randrange(-3, 7))
-            draw.text((x, y), i, font=font, fill=code_color)
-            # 随机化字符之间的距离 字符粘连可以降低识别率
-            x += font_size * random.randrange(6, 8) / 10
-
-        self.django_request.session[self.session_key] = "".join(code)
-        return image
-
-    def check(self, code):
-        """
-        检查用户输入的验证码是否正确
-        """
-        _code = self.django_request.session.get(self.session_key) or ""
-        if not _code:
-            return False
-        expires_time = self.django_request.session.get(self.captcha_expires_time) or 0
-        # 注意 如果验证之后不清除之前的验证码的话 可能会造成重复验证的现象
-        del self.django_request.session[self.session_key]
-        del self.django_request.session[self.captcha_expires_time]
-        if _code.lower() == str(code).lower() and time.time() < expires_time:
-            return True
-        else:
-            return False

utils/captcha/views.py

@@ -1,8 +0,0 @@
-from ..api import APIView
-from ..shortcuts import img2base64
-from . import Captcha
-
-
-class CaptchaAPIView(APIView):
-    def get(self, request):
-        return self.success(img2base64(Captcha(request).get()))

utils/shortcuts.py

@@ -1,8 +1,6 @@
 import os
 import random
 import re
-from base64 import b64encode
-from io import BytesIO
 
 from django.utils.crypto import get_random_string
 
@@ -38,15 +36,6 @@ def build_query_string(kv_data, ignore_none=True):
     return query_string
 
 
-def img2base64(img):
-    with BytesIO() as buf:
-        img.save(buf, "gif")
-        buf_str = buf.getvalue()
-    img_prefix = "data:image/png;base64,"
-    b64_str = img_prefix + b64encode(buf_str).decode("utf-8")
-    return b64_str
-
-
 def datetime2str(value, format="iso-8601"):
     if format.lower() == "iso-8601":
         value = value.isoformat()