build: pin celery ecosystem (kombu/billiard/vine/click/click-repl 0.3.0 等) to known-good versions from running container, fix ResolutionImpossible on floating transitive deps

backend/python/requirements.txt

@@ -17,3 +17,14 @@ celery==5.4.0
 qrcode==8.2
 pillow==12.2.0
 xskill==0.5.2
+
+# ---- pinned celery ecosystem (known-good, extracted from running container) ----
+# 避免 pip 浮动解析到与 celery 5.4.0 冲突的新版传递依赖(如 click-repl 0.2.0 的 prompt-toolkit 冲突)
+amqp==5.3.1
+kombu==5.6.2
+billiard==4.2.4
+vine==5.1.0
+click==8.4.2
+click-didyoumean==0.3.1
+click-plugins==1.1.1.2
+click-repl==0.3.0