feat(src): add initial CLI implementation

Add main entry point and scaffold CLI module to start building the tool.

- New Features:
  - Added `src/main.rs` with a hello‑world entry point.
  - Added `src/cli.rs` as placeholder for future CLI command definitions.
- Enhancements:
  - None
- Bug Fixes:
  - None

src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}