fix: restore default admin password and add reset flag

Restored 'admin123' as the default password in db init and added a -reset-admin flag to main.go.

cmd/llm-proxy/main.go

@@ -1,16 +1,22 @@
 package main
 
 import (
+	"flag"
 	"log"
+	"os"
 
 	"llm-proxy/internal/config"
 	"llm-proxy/internal/db"
 	"llm-proxy/internal/server"
 
 	"github.com/joho/godotenv"
+	"golang.org/x/crypto/bcrypt"
 )
 
 func main() {
+	resetAdmin := flag.Bool("reset-admin", false, "Reset admin password to admin123")
+	flag.Parse()
+
 	// Load environment variables
 	if err := godotenv.Load(); err != nil {
 		log.Println("No .env file found")
@@ -28,6 +34,16 @@ func main() {
 		log.Fatalf("Failed to initialize database: %v", err)
 	}
 
+	if *resetAdmin {
+		hash, _ := bcrypt.GenerateFromPassword([]byte("admin123"), 12)
+		_, err = database.Exec("UPDATE users SET password_hash = ?, must_change_password = 1 WHERE username = 'admin'", string(hash))
+		if err != nil {
+			log.Fatalf("Failed to reset admin password: %v", err)
+		}
+		log.Println("Admin password has been reset to 'admin123'")
+		os.Exit(0)
+	}
+
 	// Initialize server
 	s := server.NewServer(cfg, database)