Prevent dealers from downgrading to table size leading to overcommitment

[SharkyTheWhite]

When a dealership has shares/assistants and then changes their application table size, they might select a size which does not fit the amount anymore. This leads to a soft-lock where they are forced to kick out people before being able to correct the mistake.

Solution:
Prevent changing table size to an incompatible value.

[SharkyTheWhite]

Suggested UI change:

Disable entries in dropdown and mark them as "too small":

Only if any of the entries are marked, also show an explanation below to keep visual clutter low:

The program logic is only executed for disabling the input fields, not enforcing validation in the backend. The latter case is still handled like before: If you choose a size that does not work, you will be stuck at the "manage shares" view until you removed enough shares/assistants.

This should be sufficient to prevent dealers from downgrading too much by accident.