version: preserve semantic version separators

In this commit, we include periods in the alphabet accepted by
normalizeVerString. SemVer uses periods to separate pre-release identifiers,
but the old filter silently collapsed beta.rc1 into betarc1.

We add a focused test for the dotted RC suffix before using it for the next
release candidate.

version.go

@@ -11,7 +11,7 @@ import (
 )
 
 // semanticAlphabet
-const semanticAlphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-"
+const semanticAlphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-."
 
 // These constants define the application version and follow the semantic
 // versioning 2.0.0 spec (http://semver.org/).

version_test.go

@@ -0,0 +1,19 @@
+// Copyright (c) 2026 The btcsuite developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package main
+
+import "testing"
+
+// TestNormalizeVerString ensures valid semantic version separators are
+// preserved when normalizing pre-release and build metadata strings.
+func TestNormalizeVerString(t *testing.T) {
+	t.Parallel()
+
+	const version = "beta.rc1"
+	if got := normalizeVerString(version); got != version {
+		t.Fatalf("unexpected normalized version: got %q, want %q", got,
+			version)
+	}
+}