A2-A6: logging instead of print, claude-sonnet-5 model id, timezone-aware datetime, FastAPI lifespan, .docx parse errors -> HTTP 400

backend/main.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import os
+from contextlib import asynccontextmanager
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
@@ -24,7 +25,14 @@ allow_credentials = os.getenv('CORS_ALLOW_CREDENTIALS', 'true').strip().lower()
 if '*' in cors_origins:
     allow_credentials = False
 
-app = FastAPI(title='Vector API', version='0.1.0')
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    init_db()
+    yield
+
+
+app = FastAPI(title='Vector API', version='0.1.0', lifespan=lifespan)
 
 app.add_middleware(
     CORSMiddleware,
@@ -35,11 +43,6 @@ app.add_middleware(
 )
 
 
-@app.on_event('startup')
-def startup() -> None:
-    init_db()
-
-
 app.include_router(health_router)
 app.include_router(auth_router)
 app.include_router(analyze_router)