Fix manual glucose entry for mmol/L

[MikePlante1]

• Prevents mmol/L entry from being forced into having 1 decimal place
• Fixes typo that swapped high/low limits from mg/dL and mmol/L
• Round down for entry instead of to nearest

Addresses Issue https://github.com/nightscout/Trio/issues/339

Before this PR:

https://github.com/user-attachments/assets/f0651253-9f78-4a15-8cb7-9717c3245d56

After this PR:

https://github.com/user-attachments/assets/371ad5b7-8de6-465d-a690-18d9953cfedb

[MikePlante1]

• Can someone check localization?

  • I tried different languages and did not see the decimal/thousands place delimiters I expected
  • If confirmed, that should be a separate issue.

You have to change the Region of the phone, not the Language.

• It is a little disconcerting to enter 40.0 or 10.0 and have it modify the display to 40 or 10 respectively

  • The display on the log includes the single decimal point for mmol/L

I agree that it's not great, but unfortunately having it auto-format to a single decimal place is what messed up being able to enter double digits. I played around with it a bunch to make it so minimumFractionDigits defaults to 0, is set to 1 when the user types a decimal point, and is reset to 0 if the decimal point is deleted... but couldn't get it to work right.