fix(build): resolve ISO version from plain v* tags (e.g. v2.6)

resolve_iso_version only matched iso/v* pattern; GUI release tags
(v2, v2.1 ... v2.6) were ignored, falling back to the old v1.0.20
annotated tag via resolve_audit_version.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/build.sh

@@ -84,6 +84,15 @@ resolve_iso_version() {
             ;;
     esac
 
+    # Also accept plain v* tags (e.g. v2, v2.1 used for GUI releases)
+    tag="$(git -C "${REPO_ROOT}" describe --tags --match 'v*' --abbrev=7 --dirty 2>/dev/null || true)"
+    case "${tag}" in
+        v*)
+            echo "${tag#v}"
+            return 0
+            ;;
+    esac
+
     # Fall back to audit version so the name is still meaningful
     resolve_audit_version
 }