server-side: have a straightforward way to change the number of tables

[ApplySci]

two parts:

1. change it before the tournament starts - fairly easy - just use one of the standard templates. May need to check assigned seating numbers are contiguous 1-N.

2. change it after at least one round has been played - much more difficult. For this, we need to track substitutes, and need to reassign seating to minimise collisions. There's a crude starting point in https://github.com/ApplySci/aim/blob/main/server/run/reassign.py

[energynumbers]

part 2 is done.