fix(releases): don't drop the prerelease marker when comparing versions

A MinVer dev build on main computes a prerelease of its own guessed next
version (e.g. 2.9.1-alpha.0.14 after tag v2.9.0), which already sorts
above the last tag by numeric core, so the update banner correctly
stays quiet there. But the reduction to a bare numeric core meant a
genuine new release landing at exactly that guessed version (v2.9.1
real) compared equal to the still-running prerelease and the banner
never fired. A prerelease now only loses to a real release of the same
core, not to another prerelease of the same core.

Verified against the live repo: latest published tag is v2.9.0; a
Release build of this worktree (14 commits ahead) reports
AssemblyInformationalVersion 2.9.1-alpha.0.14+<sha>.

src/ClaudeDo.Releases/VersionComparer.cs

@@ -10,7 +10,17 @@ public static class VersionComparer
                         | !Version.TryParse(CoreVersion(current), out var cv);
 
         if (unparseable) return new VersionCompareResult(false, true);
-        return new VersionCompareResult(lv > cv, false);
+        if (lv != cv) return new VersionCompareResult(lv > cv, false);
+
+        // Same numeric core: a MinVer dev build sitting on main between two tags
+        // reports a prerelease of its own guessed *next* version (e.g. after tag
+        // v1.4.0, main computes "1.4.1-alpha.0.12" — already ahead of the tag by
+        // core, handled above). But when a real release is tagged at exactly that
+        // guessed version, the tag itself has no prerelease suffix while a still-
+        // running dev build does — that dev build must still count as older, or a
+        // genuine new release would be silently missed.
+        var isNewer = HasPrerelease(current) && !HasPrerelease(latest);
+        return new VersionCompareResult(isNewer, false);
     }
 
     // Reduce a tag/version to its numeric core: drop a leading "v", MinVer build
@@ -18,4 +28,7 @@ public static class VersionComparer
     // which System.Version can parse. So "v1.0.2-alpha+abc" -> "1.0.2".
     private static string CoreVersion(string value)
         => (value ?? "").TrimStart('v', 'V').Split('+')[0].Split('-')[0];
+
+    private static bool HasPrerelease(string value)
+        => (value ?? "").TrimStart('v', 'V').Split('+')[0].Contains('-');
 }