Refactor API structure: move chat functionality to v1 router, implement dependency injection for OpenAI client, and set up application state management

main.py

@@ -0,0 +1,30 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from api.v1.chat import router as v1_router
+from core.config import DEEPSEEK_API_KEY
+from core.llm import create_client
+
+
+app = FastAPI()
+
+# ---------------------------------------------------------------------------
+# Middleware
+# ---------------------------------------------------------------------------
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# ---------------------------------------------------------------------------
+# Singletons (stored on app.state so every module can reach them via Depends)
+# ---------------------------------------------------------------------------
+app.state.llm_client = create_client(DEEPSEEK_API_KEY)
+
+# ---------------------------------------------------------------------------
+# Routers
+# ---------------------------------------------------------------------------
+app.include_router(v1_router, prefix="/v1")