feat(battle-xp): IBattleXpService with per-mode overrides and auto level-up

- IBattleXpService.GrantAsync mutates viewer.Classes in place; caller SaveChanges
- Resolves win/loss amount from per-mode override or global XpPerWin/XpPerLoss
- Story mode ignores isWin, uses StoryXpPerClear ?? XpPerWin
- Level-up loop consults curve[row.Level].NecessaryExp; carries overflow
- Saturates at max curve level (excess piles in Exp)
- Unknown classId → no-op returning (0, 0, 1), logs Warning
- 10 unit tests (Moq-backed curve stub); DI registered next to InventoryService
- GameConfigurationJsonbTests baseline updated (19 sections)

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

SVSim.UnitTests/Models/GameConfigurationJsonbTests.cs

@@ -25,16 +25,16 @@ public class GameConfigurationJsonbTests
         var rows = await db.GameConfigs.AsNoTracking().ToListAsync();
         var byName = rows.ToDictionary(r => r.SectionName);
 
-        // One row per [ConfigSection]-marked POCO (18 sections today: Player, DefaultGrants,
+        // One row per [ConfigSection]-marked POCO (19 sections today: Player, DefaultGrants,
         // DefaultLoadout, Challenge, Rotation, PackRates, MyRotationSchedule, Story, ResourceConfig,
         // Freeplay, ArenaTwoPick, Matching, CardMasterConfig, ColosseumSeason, ColosseumRounds,
-        // LoginBonus, Guild, SkipTutorial).
+        // LoginBonus, Guild, SkipTutorial, BattleXp).
         Assert.That(byName.Keys, Is.EquivalentTo(new[]
         {
             "Player", "DefaultGrants", "DefaultLoadout", "Challenge", "Rotation", "PackRates",
             "MyRotationSchedule", "Story", "ResourceConfig", "Freeplay", "ArenaTwoPick", "Matching",
             "CardMasterConfig", "ColosseumSeason", "ColosseumRounds", "LoginBonus", "Guild",
-            "SkipTutorial",
+            "SkipTutorial", "BattleXp",
         }));
 
         var resources = JsonSerializer.Deserialize<ResourceConfig>(byName["ResourceConfig"].ValueJson)!;