Optimize Dockerfile cache, binary size, SQLite WAL, and remove unused python package

Dockerfile

@@ -1,12 +1,12 @@
 # 1. Build Go Backend
 FROM golang:1.21-alpine AS builder
-WORKDIR /app
-# TODO: go mod init & go mod download will be added later when we create the go backend code
-# COPY backend/go.mod backend/go.sum ./backend/
-# RUN cd backend && go mod download
+# Cache go modules
+COPY backend/go.mod backend/go.sum ./backend/
+RUN cd backend && go mod download
+
 COPY backend/ ./backend/
-# We'll build the go binary inside the backend dir and put it in /app/main
-RUN cd backend && CGO_ENABLED=1 go build -o /app/main main.go
+# We'll build the go binary inside the backend dir and put it in /app/main. Remove debug info for smaller binary.
+RUN cd backend && CGO_ENABLED=1 go build -ldflags="-s -w" -o /app/main main.go
 
 # 2. Final Minimal Image (Python + Go binary + Frontend)
 FROM python:3.10-slim

backend/models/db.go

@@ -39,6 +39,9 @@ func InitDB(dbPath string) {
 		log.Fatal("Failed to connect to database:", err)
 	}
 
+	// SQLite 동시성 최적화를 위해 WAL(Write-Ahead Logging) 모드를 활성화
+	DB.Exec("PRAGMA journal_mode=WAL;")
+
 	err = DB.AutoMigrate(&MediaHistory{})
 	if err != nil {
 		log.Println("Database migration error:", err)

worker/requirements.txt

@@ -1,2 +1 @@
 yt-dlp
-ffmpeg-python