feat(battle-xp): BattleXpGrantResult carries LeveledUp signal

BattleXpGrantResult gains a LeveledUp bool set true iff at least one curve
threshold was crossed during the grant (comparing pre-Level to post-Level after
the level-up loop). Callers will gate class_level_up mission emits on this flag
rather than caching pre-state themselves.

No behavior change for existing callers — they read GetXp/TotalXp/Level today
and never check LeveledUp yet. Tests cover: unchanged level → false, single
threshold → true, multi-threshold within one grant → still true, unknown class
guardrail → false.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.UnitTests/Services/BattleXpServiceTests.cs

@@ -185,7 +185,49 @@ public class BattleXpServiceTests
         Assert.That(r.GetXp, Is.EqualTo(0));
         Assert.That(r.TotalXp, Is.EqualTo(0));
         Assert.That(r.Level, Is.EqualTo(1));
+        Assert.That(r.LeveledUp, Is.False);
         Assert.That(v.Classes.Single().Exp, Is.EqualTo(0),
             "Class 1's row must not have been touched.");
     }
+
+    // ---- LeveledUp signal ----
+
+    [Test]
+    public async Task LeveledUp_is_false_when_grant_stays_within_same_level()
+    {
+        // L1 requires 100 to reach L2; grant only 40.
+        var svc = NewService(new BattleXpConfig { XpPerWin = 40 });
+        var v = NewViewerWithClass(1);
+
+        var r = await svc.GrantAsync(v, 1, isWin: true, BattleXpMode.Rank);
+
+        Assert.That(r.Level, Is.EqualTo(1));
+        Assert.That(r.LeveledUp, Is.False);
+    }
+
+    [Test]
+    public async Task LeveledUp_is_true_when_grant_crosses_a_threshold()
+    {
+        // L1=100 → grant 130 → L2 with 30 carry.
+        var svc = NewService(new BattleXpConfig { XpPerWin = 130 });
+        var v = NewViewerWithClass(1);
+
+        var r = await svc.GrantAsync(v, 1, isWin: true, BattleXpMode.Rank);
+
+        Assert.That(r.Level, Is.EqualTo(2));
+        Assert.That(r.LeveledUp, Is.True);
+    }
+
+    [Test]
+    public async Task LeveledUp_stays_true_across_multiple_bumps_in_one_grant()
+    {
+        // Grant crosses L1→L2→L3 in one go.
+        var svc = NewService(new BattleXpConfig { XpPerWin = 500 });
+        var v = NewViewerWithClass(1);
+
+        var r = await svc.GrantAsync(v, 1, isWin: true, BattleXpMode.Rank);
+
+        Assert.That(r.Level, Is.EqualTo(3));
+        Assert.That(r.LeveledUp, Is.True);
+    }
 }