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/handler/secretbox/multi.go

@@ -0,0 +1,37 @@
+package secretbox
+
+import (
+	"honoka-chan/internal/middleware"
+	"honoka-chan/internal/router"
+	secretboxschema "honoka-chan/internal/schema/secretbox"
+	"honoka-chan/internal/session"
+	honokautils "honoka-chan/internal/utils"
+
+	"github.com/gin-gonic/gin"
+)
+
+func multi(ctx *gin.Context) {
+	ss := session.Get(ctx)
+	defer ss.Finalize()
+
+	multiReq := secretboxschema.MultiReq{}
+	err := honokautils.ParseRequestData(ctx, &multiReq)
+	if ss.CheckErr(err) {
+		return
+	}
+
+	data, err := drawData(ctx, multiReq.SecretBoxID, multiReq.ID)
+	if ss.CheckErr(err) {
+		return
+	}
+
+	ss.Respond(secretboxschema.MultiResp{
+		ResponseData: data,
+		ReleaseInfo:  []any{},
+		StatusCode:   200,
+	})
+}
+
+func init() {
+	router.AddHandler("main.php", "POST", "/secretbox/multi", middleware.Common, multi)
+}