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/api/banner/list.go

@@ -1,16 +1,15 @@
 package bannerapischema
 
 type BannerList struct {
-	BannerType       int    `json:"banner_type"`
-	TargetID         int    `json:"target_id"`
-	AssetPath        string `json:"asset_path"`
-	FixedFlag        bool   `json:"fixed_flag"`
-	BackSide         bool   `json:"back_side"`
-	BannerID         int    `json:"banner_id"`
-	StartDate        string `json:"start_date"`
-	EndDate          string `json:"end_date"`
-	AddUnitStartDate string `json:"add_unit_start_date,omitempty"`
-	WebviewURL       string `json:"webview_url,omitempty"`
+	BannerType int    `json:"banner_type"`
+	TargetID   int    `json:"target_id"`
+	AssetPath  string `json:"asset_path"`
+	FixedFlag  bool   `json:"fixed_flag"`
+	BackSide   bool   `json:"back_side"`
+	BannerID   int    `json:"banner_id"`
+	StartDate  string `json:"start_date"`
+	EndDate    string `json:"end_date"`
+	WebviewURL string `json:"webview_url,omitempty"`
 }
 
 type ListData struct {