refactor(installer): use shared VersionComparer in InstallModeDetector

src/ClaudeDo.Installer/Core/InstallModeDetector.cs

@@ -33,7 +33,9 @@ public sealed class InstallModeDetector
             return new DetectedState(InstallerMode.Config, manifest, null, null);
 
         var latestVersion = release.TagName.TrimStart('v', 'V');
-        var newer = IsNewer(latestVersion, manifest.Version, out var unparseable);
+        var cmp = VersionComparer.Compare(latestVersion, manifest.Version);
+        var newer = cmp.IsNewer;
+        var unparseable = cmp.Unparseable;
         if (newer)
             return new DetectedState(InstallerMode.Update, manifest, release, latestVersion);
 
@@ -43,16 +45,4 @@ public sealed class InstallModeDetector
         };
     }
 
-    /// <summary>
-    /// Returns true only when both versions parse as System.Version (major.minor[.build[.revision]])
-    /// AND latest &gt; current. Semver pre-release tags like "0.2.0-beta" fail to parse and are
-    /// treated as "not newer" — the user drops into Config mode with no update offered, but
-    /// <paramref name="unparseable"/> is set so the UI can surface a hint.
-    /// </summary>
-    private static bool IsNewer(string latest, string current, out bool unparseable)
-    {
-        unparseable = !Version.TryParse(latest, out var lv) | !Version.TryParse(current, out var cv);
-        if (unparseable) return false;
-        return lv > cv;
-    }
 }