thirdreality: ZL1 quirk refactor baseline (savepoint before constants cleanup)

- CT mapping (142–454 ↔ 154–370) on read/write/cache
- CT snapping in u'v' and default color transition
- Perceptual brightness LUT with anti-OFF and sticky/hysteresis
- Removed XY gamut handling; kept CT snapping
- No ColorCapabilities override; quirks.v2 matching handles scope
- Detailed logging; preserved ZHA return shapes
- Fix mypy unreachable warning in nearest-CT search

Author: ekobres