Add FastAPI backend and React frontend setup with initial routes and components

backend/app/dependencies.py

@@ -0,0 +1,5 @@
+from fastapi import Header, HTTPException
+
+async def get_token_header(x_token: str = Header()):
+    if x_token != "fake-super-secret-token":
+        raise HTTPException(status_code=400, detail="X-Token header invalid")