chore: normalize line endings to LF via .gitattributes

Root-cause fix for mixed CRLF/LF in the repo (no .gitattributes previously).
Adds '* text=auto eol=lf' and explicit binary rules so all future checkouts
are LF. Renormalizes all tracked text files (no logical content change).
Backup tags: image qihuaiflow:backup-lineend-20260725-121632, git backup-lineend-pre-20260725-121632.

backend/python/requirements.txt

@@ -1,30 +1,30 @@
-# AIFlow 后端依赖
-fastapi==0.115.6
-uvicorn==0.34.0
-sqlalchemy==2.0.36
-pymysql==1.1.1
-cryptography==44.0.0
-passlib[bcrypt]==1.7.4
-python-jose[cryptography]==3.3.0
-python-multipart==0.0.18
-redis==5.2.1
-pydantic==2.10.3
-pydantic-settings==2.7.0
-python-dotenv==1.0.1
-httpx==0.28.1
-aiofiles==24.1.0
-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
+# AIFlow 后端依赖
+fastapi==0.115.6
+uvicorn==0.34.0
+sqlalchemy==2.0.36
+pymysql==1.1.1
+cryptography==44.0.0
+passlib[bcrypt]==1.7.4
+python-jose[cryptography]==3.3.0
+python-multipart==0.0.18
+redis==5.2.1
+pydantic==2.10.3
+pydantic-settings==2.7.0
+python-dotenv==1.0.1
+httpx==0.28.1
+aiofiles==24.1.0
+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