Both FilterRemind_*/RemindBeep_* option-array tokens are already
present -- and both On and Off already confirmed -- on the existing
ME7500D fixtures (issue #152), so this is a straight sibling of the
Sound/Lamp switches rather than new discovery work. Gated with
exists_fn like Lamp since the MW7300B combi dump has neither token.
Doesn't address the rest of issue #181 (power-level slider,
non-reported cooking modes, 3-level light, child lock, send-to-
microwave) -- those need write-contract confirmation this dump
doesn't carry.