fix(gacha-points): look up by odds_gacha_id, not parent_gacha_id

The two wire fields differ for seasonal packs (verified against
traffic_prod_all_gacha_exchange.ndjson — every captured request pairs
odds_gacha_id=16xxx with parent_gacha_id=10xxx). The OLD DTO docstring
assumed they were always equal; today's controller used
ParentGachaId, which lands on the base/family pack id (often a
synthesized disabled stub with no GachaPointConfig) and returns [].

Fix:
- GetGachaPointRewards and ExchangeGachaPoint now consume OddsGachaId.
- Update both DTO docstrings to document the seasonal-pack pattern.
- Regression test seeds (16015 enabled w/ GachaPointConfig, 10015
  disabled stub w/o config) and asserts the response uses 16015's
  catalog.

Symptom: opening pack 16015 (parent_gacha_id=16015 in /pack/open)
accrued gacha points correctly, but /pack/get_gacha_point_rewards with
{odds_gacha_id:16015, parent_gacha_id:10015} returned an empty list.

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

SVSim.EmulatedEntrypoint/Controllers/PackController.cs

@@ -189,7 +189,11 @@ public class PackController : SVSimController
     {
         if (!TryGetViewerId(out long viewerId)) return Unauthorized();
 
-        var rewards = await _gachaPoint.GetRewardsAsync(request.ParentGachaId, viewerId);
+        // odds_gacha_id is the active seasonal pack id (the one with GachaPointConfig +
+        // balance). parent_gacha_id is the base_pack_id of the family — not the lookup key.
+        // See GetGachaPointRewardsRequest docstring; verified against
+        // traffic_prod_all_gacha_exchange.ndjson.
+        var rewards = await _gachaPoint.GetRewardsAsync(request.OddsGachaId, viewerId);
 
         return new GetGachaPointRewardsResponse
         {
@@ -217,7 +221,9 @@ public class PackController : SVSimController
             .AsSplitQuery()
             .FirstAsync(v => v.Id == viewerId);
 
-        var outcome = await _gachaPoint.TryExchangeAsync(viewer, request.ParentGachaId, request.CardId);
+        // Use odds_gacha_id (the seasonal pack id) — that's where the balance / received marker
+        // live. Mirrors the GetGachaPointRewards fix.
+        var outcome = await _gachaPoint.TryExchangeAsync(viewer, request.OddsGachaId, request.CardId);
         if (!outcome.Success) return BadRequest(new { error = outcome.Error });
 
         await _db.SaveChangesAsync();