feat: add sentinel token generation for account creation

internal/sentinel/fnv.go

@@ -0,0 +1,21 @@
+package sentinel
+
+import "fmt"
+
+// fnv1a32 computes a 32-bit FNV-1a hash with avalanche finalizer.
+// This is a custom implementation independent of hash/fnv, matching
+// the Python reference implementation exactly.
+func FNV1a32(text string) string {
+	var h uint32 = 2166136261
+	for _, c := range text {
+		h ^= uint32(c)
+		h *= 16777619
+	}
+	// Avalanche finalizer (murmur3-style)
+	h ^= h >> 16
+	h *= 2246822507
+	h ^= h >> 13
+	h *= 3266489909
+	h ^= h >> 16
+	return fmt.Sprintf("%08x", h)
+}