Add min_brightness setting to Light Color Mapper

Adds a minimum brightness floor (default: 5) that prevents lights from
becoming too dim. Applied to both sensor brightness and default color paths.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

manifest.json

@@ -1,3 +1,3 @@
 {
-  "version": "2.2.9"
+  "version": "2.3.0"
 }