Extract ProcessTrackerService and GameLaunchService from MainWindow

[mock1ngbb]

SERVICE MIGRATION — move ~680 lines of game process tracking and launch orchestration into dedicated services.

Extract from MainWindow.axaml.cs:

• Game process tracking (process start/exit detection)
• Window focus management
• Game launch orchestration
• Game process exit handling / launcher restore

New files: Services/ProcessTrackerService.cs + Services/GameLaunchService.cs

Verification: dotnet build passes, game launch and exit detection work correctly.
Doable by: sonnet/cline-agent under 45 min.