Implement secretbox handlers and align gacha behavior

- Add secretbox API schemas, handlers, and routes for all/showDetail/pon/multi
- Load secretbox server data through the shared serverdata loader
- Fix rarity mapping and pool rules for SR/SSR/UR special boxes
- Implement thanks festival pool behavior, including UR guarantee and SSR/UR-only rates
- Correct animation-related fields such as is_hit and lowest_rarity, and add rare UR promotion animation

Signed-off-by: Sean Du <do4suki@gmail.com>

internal/schema/secretbox/multi.go

@@ -0,0 +1,19 @@
+package secretboxschema
+
+type MultiReq struct {
+	Module      string `json:"module"`
+	Action      string `json:"action"`
+	Mgd         int    `json:"mgd"`
+	ID          int    `json:"id"`
+	SecretBoxID int    `json:"secret_box_id"`
+	Count       int    `json:"count"`
+	TimeStamp   int64  `json:"timeStamp"`
+	CommandNum  string `json:"commandNum"`
+	UnitTypeIds []any  `json:"unit_type_ids"`
+}
+
+type MultiResp struct {
+	ResponseData PonData `json:"response_data"`
+	ReleaseInfo  []any   `json:"release_info"`
+	StatusCode   int     `json:"status_code"`
+}