✨ feat(cli): add run cli command

- introduce run_cli module with clap integration
- implement basic structure for future command logic

src/cli/run_cli.rs

@@ -0,0 +1,11 @@
+use clap::Parser;
+use cull_gmail::Result;
+
+#[derive(Debug, Parser)]
+pub struct RunCli {}
+
+impl RunCli {
+    pub async fn run(&self, _credential: &str) -> Result<()> {
+        Ok(())
+    }
+}