feat(hardware): parse sync packet v2 -- node MAC and health

[clonea1]

The v1 ESP-NOW sync packet carries timing only, so a node's identity on the
mesh is inferred rather than stated, and its condition is not reported at all.
Two consequences: the server guesses which node a sync came from, and a node
that is overheating, has rebooted, or is running low on heap looks identical to
a healthy one until it stops responding entirely.

v2 extends the packet to 38 bytes, adding the node's own MAC and a NodeHealth
block: die temperature, thermal state, transmit power, minimum heap seen, and
the reset reason.

The reset reason is the useful part operationally. reset_reason_name() renders
it, and rebooted_badly() distinguishes a panic or watchdog reset from a
deliberate software restart -- a node that reboots quietly and rejoins looks
healthy from the outside, and the distinction is what separates "somebody
updated it" from "it is crashing".

Version-gated so a v1 node keeps parsing exactly as before, and a padded v1
packet explicitly yields no MAC rather than reading whatever happened to sit in
those bytes. Both cases are covered by tests.

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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.