refactor: implement core and server dir to split the library and endpoints for testing

math_problems_structure/server/app.py

@@ -0,0 +1,16 @@
+from fastapi import FastAPI
+
+from math_problems_structure.server.routes import grade_1
+
+app = FastAPI(
+    title="Math Problems Structure",
+    description="HTTP server for testing math problem generators.",
+    version="0.1.0",
+)
+
+app.include_router(grade_1.router)
+
+
+@app.get("/health")
+async def health_check() -> dict[str, str]:
+    return {"status": "healthy"}