Master Issue: Finish v2 `Application` and `ConsoleDriver` architecture and remove legacy scaffolding

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This is the Master Issue is to help us track and drive to closure on finishing the v2 Application and ConsoleDriver architecture and removing the legacy scaffolding.

Context

PR #4335 successfully modernized the test infrastructure to use ApplicationImpl.Coordinator?.RunIteration() instead of the legacy MainLoop architecture. However, several legacy v1 components remain in the codebase for backward compatibility with FakeDriver. Now that FakeDriver has been updated to use the modern architecture in tests, these legacy components can be removed.

Related

• PR Fixes #4332 - Refactor test infrastructure to use modern ApplicationImpl.Coordinator instead of legacy MainLoop #4335 - Refactor test infrastructure to use modern ApplicationImpl.Coordinator
• Issue Reorganize Terminal.Gui/App Folder Structure #4329 - Original issue about FakeDriver and Application.RunIteration
• PR Fixes #4334. Propose minimal terminology improvements for Application.Run lifecycle APIs #4337 - Planned renaming work (should happen after this)
• MAINLOOP_DEEP_DIVE.md - Analysis document showing dual-architecture system