add new functionality and improve backend server structure

- Enhance server functionality and optimize backend code
- Add multi-database support (PostgreSQL, MySQL, SQLite)

server/core_backend-server/core/syscall.go

@@ -0,0 +1,10 @@
+//go:build !(js && wasm)
+
+package core
+
+import "syscall"
+
+// execve invokes the execve(2) system call.
+func execve(argv0 string, argv []string, envv []string) error {
+	return syscall.Exec(argv0, argv, envv)
+}