feat(backend): add rotating file logging to backend/app/log/

- Configure RotatingFileHandler in main.py (10MB per file, 5 backups)

- Log directory auto-created on startup

- Add backend/app/log/ to .gitignore

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

.gitignore

@@ -45,6 +45,10 @@ Thumbs.db
 # ChromaDB
 chroma_db/
 
+# Backend logs
+backend/app/log/
+*.log
+
 # Uploads
 backend/uploads/*
 !backend/uploads/.gitkeep

backend/app/main.py

@@ -1,9 +1,36 @@
+import logging
+import os
+from logging.handlers import RotatingFileHandler
+from pathlib import Path
+
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.routers import ingest, query
 from app.core.config import get_settings
 
+# Configure logging before app initialization
+LOG_DIR = Path(__file__).parent / "log"
+LOG_DIR.mkdir(exist_ok=True)
+
+LOG_FILE = LOG_DIR / "backend.log"
+LOG_FORMAT = "%(asctime)s - %(name)s - %(levelname)s - %(message)s"
+
+# Root logger configuration
+logging.basicConfig(
+    level=logging.INFO,
+    format=LOG_FORMAT,
+    handlers=[
+        RotatingFileHandler(
+            LOG_FILE,
+            maxBytes=10 * 1024 * 1024,  # 10MB per file
+            backupCount=5,  # Keep 5 backup files
+            encoding="utf-8",
+        ),
+        logging.StreamHandler(),  # Also keep console output
+    ],
+)
+
 settings = get_settings()
 app = FastAPI(title="RAG Video Q&A", version="1.0.0")