feat: initialize project structure and dependencies

- Initialize Go module with all required dependencies
- Add Makefile with build targets (all, frontend, build, clean, test, run, build-linux, build-windows)
- Create main.go skeleton with CLI flags (--addr, --data, --init)
- Add README.md with project overview and usage instructions
- Add .gitignore for bin, data, and build artifacts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+)
+
+var (
+	flagAddr    = flag.String("addr", ":9000", "Listen address")
+	flagDataDir = flag.String("data", "./data", "Data directory")
+	flagInit    = flag.Bool("init", false, "Initialize database and set password")
+)
+
+func main() {
+	flag.Parse()
+
+	fmt.Printf("GitM - Gitea Repository Sync Tool\n")
+	fmt.Printf("Listen: %s\n", *flagAddr)
+	fmt.Printf("Data: %s\n", *flagDataDir)
+
+	if *flagInit {
+		fmt.Println("Initialize mode: TODO")
+		return
+	}
+
+	log.Fatal(runServer())
+}
+
+func runServer() error {
+	return fmt.Errorf("not implemented")
+}