feat(edge): send per-slot vitals instead of discarding them at the wire

[clonea1]

update_multi_person_vitals() already computes a heart and breathing estimate
per occupancy slot, and every one of them is thrown away before transmission.
Only the aggregate packet reaches the sink, carrying a slot COUNT with no way
to see what that count was counting.

The consequence is that a host cannot distinguish "two people, both breathing
steadily" from "one person and a noisy slot that should never have been
asserted". The count alone gives no means to audit itself, so a wrong count is
indistinguishable from a right one.

This adds a 32-byte packet (EDGE_VITALS_SLOTS_MAGIC = 0xC5110009) carrying the
per-slot values, sent ALONGSIDE and never instead of the aggregate packet, so
existing sinks are unaffected and older firmware stays parseable. A sink that
does not know the magic ignores it, as with the other auxiliary packet types.

Size is asserted at compile time (_Static_assert on 32 bytes) because the
packet family shares a fixed-size wire contract and a silent struct-padding
change would corrupt every field after the first.

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Rebased onto current main before opening: staged before today's seven merges, so it needed replaying to avoid reading as a revert of them. Clean rebase, no files deleted.