Piotr observed the freeze correlates with digit '8' on the last
(units) tube position, regardless of which sensor is shown
(25.08 C, 48 %, 1018 hPa). '8' lights the most 14-seg segments of
any digit, and the units digit changes most often, so the last
position is both peak-current and the most-written-to. At brightness
15 (max) that peak current likely dips the supply / glitches the I2C
bus, which the in-ISR delay()/endTransmission() then turns into a
permanent hang.
This commit drops brightness 15 -> 4 as a cheap, reversible probe.
If freezes stop or get much rarer, the root cause is current/brownout
(fix: decoupling cap on display VCC, or separate supply, plus an I2C
bus-recovery/timeout) rather than purely the ISR timing.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
