Rebalance biome climate bands to the measured noise distribution

ClimateNoise (OpenSimplex2 FBm) concentrates temperature/humidity near 0
(measured p5..p95 = -0.54..+0.54; see mod/tools/ClimateProbe), but the biome
table's temperature bands assumed a uniform [-1.5,1.5] spread. The HOT cutoff
at 0.5 captured only 7% of the map, split four ways and gated to low
altitude, so desert/swamp/volcanic each covered under 0.5% — effectively
never seen — while COOL hogged 45%.

Recalibrated the four temperature bands to measured quantiles (~16/33/26/25%).
Every biome is now >=1% of the map:
  desert  0.40% -> 1.72%   savanna 1.73% -> 6.50%
  volcanic 0.26% -> 1.05%  swamp   0.32% -> 1.04%   tundra 10.8% -> 8.6%

Adds mod/tools/ClimateProbe for measuring the distribution; keeps
TerrainPreview's biome classifier in sync.

Author: sworcery

mod/src/main/java/com/grandterrain/worldgen/biome/GrandterrainBiomeSource.java

@@ -146,11 +146,16 @@ private float blockYToParam(int blockY) {
     private Climate.ParameterList<Holder<Biome>> buildBiomeParameters(
             float cTemperate, float cAlpine, float cMountain, float cRocky) {
 
-        Climate.Parameter T_FROZEN = Climate.Parameter.span(-1.5f, -0.3f);
-        Climate.Parameter T_COOL = Climate.Parameter.span(-0.3f, 0.15f);
-        Climate.Parameter T_WARM = Climate.Parameter.span(0.15f, 0.5f);
-        Climate.Parameter T_HOT = Climate.Parameter.span(0.5f, 1.5f);
-        Climate.Parameter T_NOT_FROZEN = Climate.Parameter.span(-0.3f, 1.5f);
+        // Bands calibrated to the MEASURED ClimateNoise distribution (FBm
+        // concentrates near 0; see mod/tools/ClimateProbe), not a uniform
+        // [-1.5,1.5]. Quantile splits ~16/33/26/25% keep every temperature
+        // tier populated — the old 0.5 HOT cutoff caught only 7% of the map
+        // and starved deserts/savannas to under 0.5% each.
+        Climate.Parameter T_FROZEN = Climate.Parameter.span(-1.5f, -0.35f);
+        Climate.Parameter T_COOL = Climate.Parameter.span(-0.35f, -0.02f);
+        Climate.Parameter T_WARM = Climate.Parameter.span(-0.02f, 0.25f);
+        Climate.Parameter T_HOT = Climate.Parameter.span(0.25f, 1.5f);
+        Climate.Parameter T_NOT_FROZEN = Climate.Parameter.span(-0.35f, 1.5f);
 
         Climate.Parameter C_LOW = Climate.Parameter.span(-1.5f, cTemperate);
         Climate.Parameter C_TEMPERATE = Climate.Parameter.span(cTemperate, cAlpine);

mod/tools/ClimateProbe.java

@@ -0,0 +1,49 @@
+import com.grandterrain.worldgen.noise.ClimateNoise;
+
+import java.util.Arrays;
+
+/**
+ * Measures the ClimateNoise temperature/humidity distribution and the share
+ * of the map that falls into each biome-table band. The bands were written
+ * assuming uniform [-1.5,1.5] noise, but FBm concentrates near 0 — this shows
+ * how lopsided the resulting biome shares really are.
+ */
+public final class ClimateProbe {
+    public static void main(String[] args) {
+        long seed = args.length > 0 ? Long.parseLong(args[0]) : 20260712L;
+        ClimateNoise cn = new ClimateNoise(seed);
+
+        int N = 1200, step = 24, off = 50000;
+        float[] temp = new float[N * N];
+        float[] humid = new float[N * N];
+        int i = 0;
+        for (int x = 0; x < N; x++)
+            for (int z = 0; z < N; z++) {
+                temp[i] = (float) cn.temperature(off + x * step, off + z * step);
+                humid[i] = (float) cn.humidity(off + x * step, off + z * step);
+                i++;
+            }
+        report("temperature", temp);
+        report("humidity", humid);
+
+        System.out.println("\ncurrent temperature bands (share of map):");
+        band("FROZEN  (-1.5..-0.3)", temp, -1.5f, -0.3f);
+        band("COOL    (-0.3..0.15)", temp, -0.3f, 0.15f);
+        band("WARM    (0.15..0.5) ", temp, 0.15f, 0.5f);
+        band("HOT     (0.5..1.5)  ", temp, 0.5f, 1.5f);
+    }
+
+    static void report(String label, float[] v) {
+        float[] s = v.clone();
+        Arrays.sort(s);
+        int n = s.length;
+        System.out.printf("%-12s min=%+.3f p5=%+.3f p10=%+.3f p25=%+.3f p50=%+.3f p75=%+.3f p90=%+.3f p95=%+.3f max=%+.3f%n",
+                label, s[0], s[n / 20], s[n / 10], s[n / 4], s[n / 2], s[3 * n / 4], s[9 * n / 10], s[19 * n / 20], s[n - 1]);
+    }
+
+    static void band(String label, float[] v, float lo, float hi) {
+        long c = 0;
+        for (float x : v) if (x >= lo && x < hi) c++;
+        System.out.printf("  %-22s %6.2f%%%n", label, 100.0 * c / v.length);
+    }
+}

mod/tools/TerrainPreview.java

@@ -85,20 +85,20 @@ public static void main(String[] args) throws Exception {
         List<Entry> entries = new ArrayList<>();
         // order matches buildBiomeParameters; ids index BIOME_NAMES
         entries.add(new Entry(-1.5f, 1.5f, -1.5f, 1.5f, cR, 1.5f, 7));          // snow_peaks
-        entries.add(new Entry(-1.5f, -0.3f, -1.5f, 1.5f, -1.5f, cR, 13));       // tundra
-        entries.add(new Entry(-0.3f, 1.5f, -1.5f, 1.5f, cM, cR, 6));            // rocky_highlands
-        entries.add(new Entry(-0.3f, 1.5f, -1.5f, 1.5f, cA, cM, 5));            // mountain_pine_forest
-        entries.add(new Entry(-0.3f, 1.5f, -1.5f, 0.3f, cT, cA, 4));            // alpine_meadow
-        entries.add(new Entry(-0.3f, 1.5f, 0.3f, 1.5f, cT, cA, 8));             // deep_valley
-        entries.add(new Entry(0.5f, 1.5f, -1.5f, -0.4f, -1.5f, cT, 9));         // volcanic
-        entries.add(new Entry(0.5f, 1.5f, -0.4f, -0.2f, -1.5f, cT, 10));        // desert
-        entries.add(new Entry(0.5f, 1.5f, -0.2f, 0.4f, -1.5f, cT, 11));         // savanna
-        entries.add(new Entry(0.5f, 1.5f, 0.4f, 1.5f, -1.5f, cT, 12));          // swamp
-        entries.add(new Entry(0.15f, 0.5f, 0.4f, 1.5f, -1.5f, cT, 15));         // dark_forest
-        entries.add(new Entry(0.15f, 0.5f, 0.0f, 0.4f, -1.5f, cT, 3));          // temperate_forest
-        entries.add(new Entry(0.15f, 0.5f, -1.5f, 0.0f, -1.5f, cT, 2));         // lowland_plains
-        entries.add(new Entry(-0.3f, 0.15f, 0.2f, 1.5f, -1.5f, cT, 14));        // birch_forest
-        entries.add(new Entry(-0.3f, 0.15f, -1.5f, 0.2f, -1.5f, cT, 2));        // lowland_plains
+        entries.add(new Entry(-1.5f, -0.35f, -1.5f, 1.5f, -1.5f, cR, 13));      // tundra
+        entries.add(new Entry(-0.35f, 1.5f, -1.5f, 1.5f, cM, cR, 6));           // rocky_highlands
+        entries.add(new Entry(-0.35f, 1.5f, -1.5f, 1.5f, cA, cM, 5));           // mountain_pine_forest
+        entries.add(new Entry(-0.35f, 1.5f, -1.5f, 0.3f, cT, cA, 4));           // alpine_meadow
+        entries.add(new Entry(-0.35f, 1.5f, 0.3f, 1.5f, cT, cA, 8));            // deep_valley
+        entries.add(new Entry(0.25f, 1.5f, -1.5f, -0.4f, -1.5f, cT, 9));        // volcanic
+        entries.add(new Entry(0.25f, 1.5f, -0.4f, -0.2f, -1.5f, cT, 10));       // desert
+        entries.add(new Entry(0.25f, 1.5f, -0.2f, 0.4f, -1.5f, cT, 11));        // savanna
+        entries.add(new Entry(0.25f, 1.5f, 0.4f, 1.5f, -1.5f, cT, 12));         // swamp
+        entries.add(new Entry(-0.02f, 0.25f, 0.4f, 1.5f, -1.5f, cT, 15));       // dark_forest
+        entries.add(new Entry(-0.02f, 0.25f, 0.0f, 0.4f, -1.5f, cT, 3));        // temperate_forest
+        entries.add(new Entry(-0.02f, 0.25f, -1.5f, 0.0f, -1.5f, cT, 2));       // lowland_plains
+        entries.add(new Entry(-0.35f, -0.02f, 0.2f, 1.5f, -1.5f, cT, 14));      // birch_forest
+        entries.add(new Entry(-0.35f, -0.02f, -1.5f, 0.2f, -1.5f, cT, 2));      // lowland_plains
 
         double[][] height = new double[n][n];
         int[][] biome = new int[n][n];