chore: 将后端移动到 api/ 目录，准备合并为单仓库

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/requirements.txt

@@ -0,0 +1,61 @@
+annotated-types==0.7.0
+anyio==4.12.1
+asgiref==3.11.0
+attrs==25.4.0
+autobahn==25.12.2
+automat==25.4.16
+cbor2==5.8.0
+certifi==2026.2.25
+cffi==2.0.0
+channels==4.3.2
+channels-redis==4.3.0
+click==8.3.1
+constantly==23.10.4
+cryptography==46.0.3
+daphne==4.2.1
+distro==1.9.0
+django==6.0.1
+django-cors-headers==4.9.0
+django-extensions==4.1
+django-ninja==1.5.3
+django-redis==6.0.0
+dnspython==2.8.0
+email-validator==2.3.0
+gunicorn==24.1.1
+h11==0.16.0
+httpcore==1.0.9
+httptools==0.7.1
+httpx==0.28.1
+hyperlink==21.0.0
+idna==3.11
+incremental==24.11.0
+jiter==0.13.0
+msgpack==1.1.2
+openai==2.24.0
+packaging==26.0
+psycopg==3.3.2
+psycopg-binary==3.3.2
+py-ubjson==0.16.1
+pyasn1==0.6.2
+pyasn1-modules==0.4.2
+pycparser==3.0
+pydantic==2.12.5
+pydantic-core==2.41.5
+pyopenssl==25.3.0
+python-dotenv==1.2.1
+pyyaml==6.0.3
+redis==7.1.0
+service-identity==24.2.0
+sniffio==1.3.1
+sqlparse==0.5.5
+tqdm==4.67.3
+twisted==25.5.0
+txaio==25.12.2
+typing-extensions==4.15.0
+typing-inspection==0.4.2
+ujson==5.11.0
+uvicorn==0.40.0
+uvloop==0.22.1
+watchfiles==1.1.1
+websockets==16.0
+zope-interface==8.2