experiment(render): revert BLUE shift; warm WHITE palette to (255,248,230)

#5 (BLUE → [8,32,220]) made sky map to WHITE which dithered greenish.
Reverting BLUE to baseline (24,64,192).

#6: warm WHITE from (245,245,240) → (255,248,230). Slight cream shift
pulls warm-toned skin pixels toward WHITE in the nearest-color match
before error diffusion has a chance to drift them toward BLUE. Sky
mapping unchanged (still maps to BLUE). Cost: real off-white pixels
might quantize toward a slightly warmer cream — should be subtle.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/MessageHandler/RenderImageMessageHandler.php

@@ -21,20 +21,22 @@ final class RenderImageMessageHandler
     /**
      * Waveshare Spectra 6 palette. Values are the dither's *mapping targets* —
      * panel still displays each nibble as its actual ink colour regardless of
-     * what RGB we tell the algorithm. Shifting BLUE further from neutral pulls
-     * borderline-bluish pixels (sky cast on skin) toward RED/WHITE/YELLOW.
+     * what RGB we tell the algorithm.
      *
      * Baseline (frozen at render-baseline-2026-05-14):
+     *   0x1 WHITE = [245, 245, 240]
      *   0x5 BLUE  = [24, 64, 192]
-     * Experiment #5:
-     *   0x5 BLUE  = [ 8, 32, 220]  — more saturated mapping target.
+     * Experiment #5 (BLUE → [8, 32, 220]) — made sky greenish, reverted.
+     * Experiment #6 (WHITE → [255, 248, 230]) — warmer cream pulls warm
+     *   skin pixels toward WHITE before error diffusion can drift them
+     *   toward BLUE, without changing how sky maps.
      */
     public const PALETTE = [
         0x0 => [26,  26,  26 ],  // BLACK
-        0x1 => [245, 245, 240],  // WHITE
+        0x1 => [255, 248, 230],  // WHITE (warmed in experiment #6)
         0x2 => [240, 208, 0  ],  // YELLOW
         0x3 => [192, 48,  32 ],  // RED
-        0x5 => [8,   32,  220],  // BLUE (shifted in experiment #5)
+        0x5 => [24,  64,  192],  // BLUE
         0x6 => [16,  160, 64 ],  // GREEN
     ];