chore: add cmd/doplan/main.go to repository

- Main entry point for DoPlan CLI
- Required for building binaries in release workflow
- File was missing from git repository

Author: iDorgham

cmd/doplan/main.go

@@ -0,0 +1,12 @@
+package main
+
+import (
+	"github.com/doplan/cli/internal/cli"
+)
+
+func main() {
+	// DoPlan CLI - Entry point
+	// Execute the root Cobra command
+	cli.Execute()
+}
+