Is your feature request related to a problem? Please describe.

as described in #2698, it needs easier-to-read label names for human.
number(0-9) is not allowed in current rule so it needs to use alphabetical numbers.
it makes too hard to read/distinguish for human.

for example, regulation names use numbers.
names of series(generation, season), models also often use numbers or YEAR in YYYY

restricted-NN-years-old is not allowed then
restricted-eighteen-years-old
restricted-thirteen-years-old

how about name of ISO standard with 5 digits?
model-twothousands-twentyfour  instead of model-2024?

Describe the solution you'd like

relax label naming rule in atproto/api.

Describe alternatives you've considered

no alternatives easier than the above.

Additional context