Add optional process name configuration for improved game stopping

[Copilot]

This PR addresses the suboptimal game stopping mechanism by adding support for an optional stopProcessName configuration field that enables more reliable game termination, particularly for Steam/Epic launcher games.

Problem

Previously, GABS could only stop the processes it directly launched. For Steam/Epic games, this meant only the launcher process could be stopped, not the actual game process that runs independently. This left games running even after calling games.stop or games.kill.

Solution

Added an optional stopProcessName field to game configurations that allows users to specify the actual process name to terminate:

{
  "rimworld": {
    "launchMode": "SteamAppId", 
    "target": "294100",
    "stopProcessName": "RimWorldWin64.exe"
  },
  "minecraft": {
    "launchMode": "DirectPath",
    "target": "/opt/minecraft/start.sh", 
    "stopProcessName": "java"
  }
}

Implementation Details

• Cross-platform process finding: Uses tasklist on Windows, ps on macOS/Linux
• Graceful fallback: If process name stopping fails, falls back to original process stopping
• Both stop modes: Works with both games.stop (graceful) and games.kill (force)
• CLI integration: Interactive game setup now prompts for optional stop process name
• Backward compatibility: Existing configurations continue working without changes

Platform Support

Platform	Process Discovery	Process Termination
Windows	tasklist /FO CSV	taskkill [/F] /PID
macOS	ps axo pid,comm	kill [-9] <pid>
Linux	ps axo pid,comm	kill [-9] <pid>

The implementation handles platform-specific executable naming (e.g., adding .exe on Windows) and supports both exact matches and partial name matching for flexibility.

Fixes #18.

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