Vendor correction of the fallback framing

COLDCARD publicly correcting Jack Mallers over the description of a weak entropy fallback, and the clearest vendor statement held of how the defect arose. It says Yasmarang was not Coinkite's fallback but MicroPython's built-in general-purpose RNG, added upstream in May 2018, and that it did not enter Coldcard's seed generation until the libNgU migration in March 2021. It argues the design intent was the opposite of a software fallback: seed generation was to rely on the hardware TRNG alone, and setting MICROPY_HW_ENABLE_RNG=0 was meant to disable the software path, but the symbol instead resolved to the runtime's default, so the behaviour was inherited from the platform through a link-time error rather than chosen. Mallers's severity alert is held at mallers-coldcard-alert, and the guard and generator themselves are tracked as repository sources. The statement of intent is the vendor's own account of its own work.