Code Cleanup – tool to move all using statements inside namespace in all cs files in my solution?

With Resharper it can be done in two steps.

1. Set the checkbox “Add ‘using’ directive to the deepest scope” in Code Editing → C# → Code Style → Reference qualification.
   

2. In the context menu of the solution choose “Cleanup Code…”.
   

You might want to create a custom cleanup pofile that suits your needs before performing the cleanup.

In ReSharper before v9 the setting is located somewhere else: