feat(cesium): ease off the watercolour vibrance + softer buildings

- post-process: add a luminance desaturate (~28%) and soften the posterize from
6 to 8 levels (+ lighter edge darkening) so the globe reads less aggressively
- OSM buildings: lower wash opacity and add a height band so towers blend into
the painterly map as translucent forms instead of solid colour blocks

index.html

@@ -4832,10 +4832,13 @@
         defines: { h: "${feature['cesium#estimatedHeight']}" },
         color: {
           conditions: [
-            ["${h} >= 120", "color('" + c[0] + "', 0.85)"],
-            ["${h} >= 60", "color('" + c[1] + "', 0.8)"],
-            ["${h} >= 25", "color('" + c[2] + "', 0.78)"],
-            ["true", "color('" + c[3] + "', 0.7)"],
+            // softer, more translucent washes so towers read as painted forms
+            // that blend with the map rather than solid colour blocks
+            ["${h} >= 140", "color('" + c[0] + "', 0.72)"],
+            ["${h} >= 80",  "color('" + c[1] + "', 0.66)"],
+            ["${h} >= 45",  "color('" + c[2] + "', 0.6)"],
+            ["${h} >= 20",  "color('" + c[2] + "', 0.54)"],
+            ["true", "color('" + c[3] + "', 0.48)"],
           ],
         },
       });
@@ -4961,12 +4964,14 @@
                   void main() {
                     vec2 uv = v_textureCoordinates;
                     vec3 c = texture(colorTexture, uv).rgb;
-                    c = floor(c * 6.0 + 0.5) / 6.0;            // flat washes
+                    c = floor(c * 8.0 + 0.5) / 8.0;            // softer washes (was 6 - less flat)
+                    float luma = dot(c, vec3(0.299, 0.587, 0.114));
+                    c = mix(vec3(luma), c, 0.72);             // ease off the vibrance (~28% desaturate)
                     float o = 1.0 / 1024.0;
                     vec3 dx = texture(colorTexture, uv+vec2(o,0.)).rgb - texture(colorTexture, uv-vec2(o,0.)).rgb;
                     vec3 dy = texture(colorTexture, uv+vec2(0.,o)).rgb - texture(colorTexture, uv-vec2(0.,o)).rgb;
                     float edge = clamp(length(dx)+length(dy), 0.0, 1.0);
-                    out_FragColor = vec4(c * (1.0 - 0.35*edge), 1.0);
+                    out_FragColor = vec4(c * (1.0 - 0.3*edge), 1.0);
                   }`,
               }));
             } catch (e) { console.warn("[cesium] watercolor post-process failed", e); }