feat: users can restore Jan app to `factory settings` in Settings

[0xSage]

Problem

• when we ship breaking changes, sometimes the /models assistant folders need to be overwritten/deleted/purged
• I have to manually reset app right now
• Edge case: #1072
• rm -rf /application support
• rm -rf /janroot

Success Criteria A clear and concise description of what you want to happen.

• A "danger!" factory reset button in settings to make this step easier for users
• All models, assistants, threads folders are reset to what you would get via a new installation
• Delete cache & app support folders

Additional context Add any other context or screenshots about the feature request here.