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/Models/Dtos/Requests/Pack/ExchangeGachaPointRequest.cs

@@ -4,6 +4,11 @@ using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
 
 namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.Pack;
 
+/// <summary>
+/// Inbound /pack/exchange_gacha_point body. See
+/// <see cref="GetGachaPointRewardsRequest"/> for the odds_gacha_id vs parent_gacha_id split —
+/// same pattern here: the server consumes <c>odds_gacha_id</c> for the lookup.
+/// </summary>
 [MessagePackObject]
 public class ExchangeGachaPointRequest : BaseRequest
 {