Release v0.12.3

Water temperature colours (thermometer in PumpVisual, readout in
PumpScheduler) now follow the koi temperature bands from the new research
instead of a neutral cold->warm gradient (graphics.tempColor):
<2 red · 2-4 orange · 4-8 blue (winter rest) · 8-13 amber (the cold
"Aeromonas window": pathogens active, immune system not) · 13-17 teal ·
17-23 light green · 23-26 green (growth optimum) · 26-28 light green ·
28-30 orange · >=30 red.

Per-actuator wheel colours: the Scheduler widget's "Actuators" settings now
give every actuator its own on/off colour picker (stored per actuator in
actuatorColors), replacing the single global pair from v0.12.2. The
wheel's darker gradient shade is still derived automatically.

Research + handbook:

• New doc/research/wassertemperaturen-im-koiteich.md (faithful transcription
  of the 14-page koi-temperature study, with the source list T1-T93).
• The German handbook now carries BOTH research papers as Anhang 1 & 2,
  appended at build time by scripts/build-handbook-pdf.mjs (single source of
  truth in doc/research/) — DE manual PDF now 41 pages. The English handbook
  gets an appendix note pointing to them. Widget/handbook thermometer text
  updated to the koi-comfort colour meaning.

README + news (11 languages).

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com