Add launcher_log.txt support for stdout/stderr logging

[Copilot]

Summary

This PR implements support for launcher_log.txt to capture stdout and stderr from Minecraft processes, matching the behavior of the vanilla Minecraft launcher.

Changes

Modified xmcl-runtime/launch/LaunchService.ts to:

• Create a launcher_log.txt file in the game directory when launching Minecraft
• Stream both stdout and stderr output to the file in real-time
• Properly close the file stream when the game exits or encounters an error
• Handle stream errors gracefully to prevent crashes

Implementation Details

When a Minecraft process is launched, the launcher now:

1. Creates the log file: A launcher_log.txt file is created in the game directory (instance path) using a write stream
2. Captures all output: Both stdout and stderr are written to the file as they are received from the Minecraft process
3. Handles errors: Stream errors (e.g., permission issues, disk space) are caught and logged without crashing the application
4. Cleans up properly: The file stream is closed when the game exits normally or when an error occurs

Behavior

.minecraft/
├── launcher_log.txt  ← New file created on each launch
├── logs/
├── saves/
└── ...

Each new launch overwrites the previous launcher_log.txt file, matching vanilla Minecraft launcher behavior. This makes it easier for users and developers to debug launch issues.

Fixes the issue described in #[issue_number] where the launcher was missing this standard Minecraft logging feature.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Support laucnher_log.txt for stdout</issue_title>
<issue_description>The vanilla Minecraft launcher will emit a laucnher_log.txt for launch. We need to implement the same thing. And we should consider the stderr log to.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #1112

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