Fixes iOS zoom issue

[axelknock]

On iOS there is a common feature on all browsers where inputs with text under a certain size cause the view to zoom in to compensate. On a Progressive Web App this zoom cannot be reverted, requiring the app to be re-opened.
This pull request simply sets the inputs I found to have relative sizes to fixed 16px size to prevent the issue from happening.

Demonstration of the issue:
https://github.com/almarklein/timetagger/assets/72520178/48c91ccb-d626-4b03-9f1a-8494e470de5c

[almarklein]

There's another one a few lines down (for duration). I think these are all of 'm.

[axelknock]

I changed the further dialog. I also confirmed that there were no other cases of percentage sizing of text inputs:

Exported grep results:

timetagger/common/cred.html:98:            <input id='input_u' type='text' placeholder='username' /><br />
timetagger/pages/login.md:69:<input id='input_u' type='text' placeholder='username' style='margin:4px;'/><br />
timetagger/app/dialogs.py:676:                <input type='text' style='flex:1; min-width: 50px; font-size: 16px;' />
timetagger/app/dialogs.py:684:                <input type='text' style='flex:1; min-width: 50px; font-size: 16px;' />
timetagger/app/dialogs.py:691:            <input type='text' style='flex: 1; min-width: 50px; font-size: 16px' />
timetagger/app/dialogs.py:1524:                <input type='text' style='width:100%;' spellcheck='true' />
timetagger/app/dialogs.py:2005:            <input type='text' style='width: 100px; border: 5px solid #eee' spellcheck='false' />
timetagger/app/dialogs.py:2276:                <input type='text' spellcheck='false' />
timetagger/app/dialogs.py:2421:                <input type='text' style='width:100%;' spellcheck='false' />

I also went through the interface on mobile looking for input fields that caused the zoom issue and could find none. I also found that loading a browser through the PWA (by selecting the guide for example) caused the display to refresh, so that can work as an alternative to restarting.

[almarklein]

Thanks for this contribution, and for taking the time to search for more cases!