fix: init VBLoRA bank B with small noise

Author: ooples

src/LoRA/Adapters/VBLoRAAdapter.cs

@@ -349,13 +349,20 @@ private void InitializeBanksIfNeeded(int inputSize, int outputSize)
         if (!_globalBankB.ContainsKey(_bankKey))
         {
             Matrix<T> bankB = new Matrix<T>(_bankSizeB, outputSize);
+            T stddev = NumOps.Multiply(
+                NumOps.Sqrt(NumOps.Divide(NumOps.One, NumOps.FromDouble(_bankSizeB))),
+                NumOps.FromDouble(0.01));
 
-            // Initialize with zeros (so adapters start with no effect, like standard LoRA B matrix)
+            // Initialize with small Gaussian random values so both A and B receive gradient signal immediately.
             for (int i = 0; i < _bankSizeB; i++)
             {
                 for (int j = 0; j < outputSize; j++)
                 {
-                    bankB[i, j] = NumOps.Zero;
+                    // Box-Muller transform for Gaussian random numbers
+                    double u1 = Random.NextDouble();
+                    double u2 = Random.NextDouble();
+                    double randStdNormal = Math.Sqrt(-2.0 * Math.Log(u1)) * Math.Sin(2.0 * Math.PI * u2);
+                    bankB[i, j] = NumOps.Multiply(NumOps.FromDouble(randStdNormal), stddev);
                 }
             }