Better onboarding

### Checks

- [x] I have read the Wiki, searched the open issues, and still think this is a new feature.

### Explain the problem clearly and succinctly:

Users are complaining that the educational hints are too intrusive.

### Describe the solution you'd like:

Add an onboarding process at startup to explain the main features and give users the option to disable the educational hints at that point.

### Describe alternatives you've considered:

_No response_

### Additional context:

_No response_

Start by reviewing the existing educational hints and the startup flow to understand where onboarding belongs. Define the main features to explain and the point where users can disable hints; the work is done when onboarding appears at startup and the preference reliably prevents those hints.

Written by the indexing model from the issue text.