*IMPORTANT* Refactor the treatmentplan calculator

The current version of the treatment plans are not very good. We need to:
- make it more dynamic. If the user for example installes the app and do the onboarding at 12:00, then the plan must start from whenever the user take s their first dose AFTER the onboarding, we cant wait unit next day or some set time, it starts whenever the user decides to start, and every following dose time must be dependend on the previus one, not some set in stone treatment plan. I guess what im trying to say is that the planmust be dynamic and responsive to what the user does, always.
- We also need to refactor the model itself, it seems a little wild that I sometimes wait like 2 hours and sometimes less then one hour... It just not working properly and I think alot of the stems from it being too rigid and working from a treatmentplan that gets set by the onboardin and then is treated as the only truth

Start by locating the treatment plan calculator and the onboarding flow, then trace how the initial dose and following dose times are selected. Done means the plan begins after the user's first post-onboarding dose, derives each subsequent dose from the previous one, and responds to user actions rather than a fixed onboarding plan.

Written by the indexing model from the issue text.