feat(frontend+backend): connect api backend with frontend

backend/requirements.txt

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+annotated-types==0.7.0
+anyio==4.10.0
+click==8.2.1
+fastapi==0.116.1
+h11==0.16.0
+httptools==0.6.4
+idna==3.10
+pydantic==2.11.7
+pydantic_core==2.33.2
+python-dotenv==1.1.1
+PyYAML==6.0.2
+sniffio==1.3.1
+starlette==0.47.3
+typing-inspection==0.4.1
+typing_extensions==4.15.0
+uvicorn==0.35.0
+uvloop==0.21.0
+watchfiles==1.1.0
+websockets==15.0.1