docs: add Coldcard Mk2/Mk3 seed-entropy security warning to README - #524

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nrobi144 wants to merge 3 commits into

caravan-bitcoin:mainfrom

nrobi144:coldcard-mk3-warning

Commits on Aug 6, 2026

docs: warn about Coldcard Mk3 seed-entropy advisory (Coinkite, Jul 2026)
nrobi144
committed
e45164a
Remove unicode from Coldcard warning (use plain ASCII)
nrobi144
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5e2fc95

Commits on Aug 7, 2026

Correct firmware/model details per Coinkite advisory (Mk2/Mk3 4.0.1-4.1.9, add Mk5)
nrobi144
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dbd697b