perf(pixiv): 改用 waitress 线程池，缓存路径改为相对路径

- IMAGE_DIR 由硬编码 /home/pixiv/images 改为 (Path(__file__).parent/'../cache/pixiv/images').resolve()
  （即 source/cache/pixiv/images），mkdir 补 parents=True
- systemd/pixiv.service: ExecStart 改为 waitress-serve --host=127.0.0.1 --port=9007 --threads=8 pixiv:app
  替代 Flask 开发服务器（thread-per-request 无上限，突发流量下线程爆炸）
- __main__ 兜底加 threaded=True，手动运行时不串行

source/pixiv/pixiv.py

@@ -12,8 +12,8 @@ USER_AGENT = "PixivIOSApp/7.13.0 (iOS 14.6; iPhone)"
 
 urllib3.disable_warnings()
 
-IMAGE_DIR = Path("/home/pixiv/images")
-IMAGE_DIR.mkdir(exist_ok=True)
+IMAGE_DIR = (Path(__file__).resolve().parent / "../cache/pixiv/images").resolve()
+IMAGE_DIR.mkdir(parents=True, exist_ok=True)
 
 app = Flask(__name__)
 
@@ -196,4 +196,4 @@ if __name__ == '__main__':
         else:
             print("Warning: access_token missing in tokens.json")
     print(f"Cache directory: {IMAGE_DIR}")
-    app.run(host='0.0.0.0', port=9088, debug=False)
+    app.run(host='127.0.0.1', port=9007, debug=False, threaded=True)

systemd/pixiv.service

@@ -8,7 +8,7 @@ Type=simple
 User=root
 WorkingDirectory=/home/openapi/source/pixiv
 Environment=PATH=/home/openapi/env/general/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
-ExecStart=/home/openapi/env/general/bin/python /home/openapi/source/pixiv/pixiv.py
+ExecStart=/home/openapi/env/general/bin/waitress-serve --host=127.0.0.1 --port=9007 --threads=8 pixiv:app
 Restart=always
 RestartSec=5
 StandardOutput=append:/var/log/pixiv.log