feat: move settings.json to .config on unix-like systems

[lucaengelhard]

Description

Currently the settings are saved next to the program state files on unix-like machines. This PR moves the settings.json file so that it aligns with the .config convention.

Type of Change

• Bug fix
• New feature
• Breaking change
• Performance improvement
• Code refactoring
• Documentation update
• UI/UX improvement
• Build/CI or Dependency update

Changes Made

• update get_settings_path so that it resolves to .config/RapidRaw/settings.json on unix-like systems
• added migration logic so that old settings.json are correctly transferred

Screenshots/Videos

Testing

• I have tested these changes locally and confirmed that they work as expected without issues

Test Configuration:

• OS: Omarchy 3.4.1 (Linux 6.18.13-arch1-1)
• Hardware: NVIDIA RTX 4060, Intel i5-11400F

Checklist

• My code follows the project's code style
• I haven't added unnecessary AI-generated code comments
• My changes generate no new warnings or errors

Additional Notes

Old settings.json files are automatically moved. Maybe there should be a warning or popup that asks if the user wants the file moved?

Also the folder name is currently hardcoded in. That maybe should be changed?

AI Disclaimer:

Please state the involvement of AI in this PR:

• This PR is entirely AI-generated
• This PR is AI-generated but guided by a human
• This PR was handwritten with AI assistance (spell check, logic suggestions, error resolving)
• This PR contains only blood, sweat, and coffee (AI-free)

[lucaengelhard]

Maybe it also would be a good idea to separate things like lastFolderState into a different file, because that isn't relevant for the config and only store real settings data in the config