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.Database/Services/BattleXp/BattleXpService.cs

@@ -0,0 +1,79 @@
+using Microsoft.Extensions.Logging;
+using SVSim.Database.Models;
+using SVSim.Database.Models.Config;
+using SVSim.Database.Repositories.Globals;
+
+namespace SVSim.Database.Services.BattleXp;
+
+public sealed class BattleXpService : IBattleXpService
+{
+    private readonly IGlobalsRepository _globals;
+    private readonly IGameConfigService _config;
+    private readonly ILogger<BattleXpService> _log;
+
+    // Curve is immutable per boot; cache the first fetch.
+    private List<ClassExpEntry>? _cachedCurve;
+
+    public BattleXpService(IGlobalsRepository globals, IGameConfigService config, ILogger<BattleXpService> log)
+    {
+        _globals = globals;
+        _config = config;
+        _log = log;
+    }
+
+    public async Task<BattleXpGrantResult> GrantAsync(
+        Viewer viewer, int classId, bool isWin, BattleXpMode mode, CancellationToken ct = default)
+    {
+        var row = viewer.Classes.FirstOrDefault(c => c.Class.Id == classId);
+        if (row is null)
+        {
+            _log.LogWarning(
+                "BattleXpService: viewer {ViewerId} has no ViewerClassData for classId {ClassId}; skipping grant.",
+                viewer.Id, classId);
+            return new BattleXpGrantResult(0, 0, 1);
+        }
+
+        int amount = ResolveAmount(mode, isWin);
+        row.Exp += amount;
+
+        var curve = _cachedCurve ??= await _globals.GetClassExpCurve();
+        // curve[level] semantics: XP required WHILE AT that level to reach the next
+        // (matching classexp.csv seed values and LoadController's client-facing shape).
+        var byLevel = curve.ToDictionary(e => e.Id, e => e.NecessaryExp);
+        int maxLevel = curve.Count == 0 ? row.Level : curve.Max(e => e.Id);
+
+        while (row.Level < maxLevel
+               && byLevel.TryGetValue(row.Level, out var needed)
+               && row.Exp >= needed)
+        {
+            row.Exp -= needed;
+            row.Level += 1;
+        }
+
+        return new BattleXpGrantResult(amount, row.Exp, row.Level);
+    }
+
+    private int ResolveAmount(BattleXpMode mode, bool isWin)
+    {
+        var cfg = _config.Get<BattleXpConfig>();
+
+        if (mode == BattleXpMode.Story)
+            return cfg.StoryXpPerClear ?? cfg.XpPerWin;
+
+        int? overrideVal = (mode, isWin) switch
+        {
+            (BattleXpMode.Practice,     true)  => cfg.PracticeXpPerWin,
+            (BattleXpMode.Practice,     false) => cfg.PracticeXpPerLoss,
+            (BattleXpMode.Rank,         true)  => cfg.RankXpPerWin,
+            (BattleXpMode.Rank,         false) => cfg.RankXpPerLoss,
+            (BattleXpMode.Free,         true)  => cfg.FreeXpPerWin,
+            (BattleXpMode.Free,         false) => cfg.FreeXpPerLoss,
+            (BattleXpMode.ArenaTwoPick, true)  => cfg.ArenaTwoPickXpPerWin,
+            (BattleXpMode.ArenaTwoPick, false) => cfg.ArenaTwoPickXpPerLoss,
+            (BattleXpMode.Colosseum,    true)  => cfg.ColosseumXpPerWin,
+            (BattleXpMode.Colosseum,    false) => cfg.ColosseumXpPerLoss,
+            _ => null,
+        };
+        return overrideVal ?? (isWin ? cfg.XpPerWin : cfg.XpPerLoss);
+    }
+}