Add user prompt to optionally skip tutorial on first launch

### Describe your improvement idea or feature request

Currently, when a user opens the Taskwarrior Flutter app for the first time, the tutorial/onboarding flow is shown automatically without asking for user consent.

While this is helpful for new users, it can feel intrusive for experienced users who may prefer to skip the tutorial and start using the app immediately.

Adding a prompt that asks users whether they want to view the tutorial would improve flexibility and user experience.

### How would you like to see it implemented?

1. On the first app launch, show a prompt such as: “Would you like to see the tutorial?”
2. Yes → Start the existing tutorial flow
3. No / Skip → Navigate directly to the main app screen
4. Store the user’s choice so:
- The prompt is not shown again
- The tutorial does not auto-start unless explicitly chosen

### Put here any screenshots or videos (optional)

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### How can we contact you (optional)

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### Would you like to work on this issue?

Yes

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- [x] I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.