Add input automation

[botoddly]

Summary

• add a synchronous application-lifetime IInputAutomation service for synthetic mouse, keyboard, and text input
• support window-local move-to coordinates and delta-based relative movement while preserving existing input state and dispatch semantics
• normalize SDL input before it reaches input services so native and automated input share the same path
• document the API and cover routing, movement, click ordering, state transitions, text input, and invalid view scopes

Testing

• dotnet test Pixely.slnx --no-restore