ArrayTrain: BIC-selected unbounded θ mixtures + HWE-guided labelling

Fixed θ windows mislabelled compressed/asymmetric loci (2-cluster loci: 1418 vs
186 errors). Now 1/2/3-component mixtures chosen by BIC, labelled by HWE
goodness of fit plus weak position and gap priors, split clusters merged.
GSE165845 chr22 vs 1000G 30x (240 arrays): concordance 99.44 % (v1 99.27 %,
vendor EGT 99.46 %), NRD 1.30 % (1.89 %, 1.23 %), call rate 99.61 %.
docs/validation/V2_arraytrain.md, K-030; plan §12, CLI-038.

docs/validation/V2_arraytrain_gse165845.json

@@ -0,0 +1,28 @@
+{
+ "dataset": "GSE165845 GSA v1 (C2 build-38 BPM); train = replicate 3 (120 arrays), evaluate = replicates 1-2 (240 arrays)",
+ "truth": "1000G NYGC 30x phased panel, chr22 SNVs on the array",
+ "egt_v1_fixed_windows": {
+  "chrom": "22",
+  "samples": 240,
+  "truth_sites": 8278,
+  "call_rate": 0.9947053434807118,
+  "concordance": 0.9926765907658587,
+  "nrd": 0.018946074088334416
+ },
+ "egt_v2_bic_hwe": {
+  "chrom": "22",
+  "samples": 240,
+  "truth_sites": 8278,
+  "call_rate": 0.9960623540307643,
+  "concordance": 0.9943676222304063,
+  "nrd": 0.013034595450012981
+ },
+ "vendor_gsa_v1_c1_egt": {
+  "chrom": "22",
+  "samples": 240,
+  "truth_sites": 8278,
+  "call_rate": 0.9915201940887493,
+  "concordance": 0.9945781643910259,
+  "nrd": 0.012251034586575862
+ }
+}