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/handler.go

@@ -6,6 +6,7 @@ import (
 	_ "honoka-chan/internal/handler/api"
 	_ "honoka-chan/internal/handler/award"
 	_ "honoka-chan/internal/handler/background"
+	_ "honoka-chan/internal/handler/banner"
 	_ "honoka-chan/internal/handler/download"
 	_ "honoka-chan/internal/handler/event"
 	_ "honoka-chan/internal/handler/eventscenario"
@@ -25,6 +26,7 @@ import (
 	_ "honoka-chan/internal/handler/profile"
 	_ "honoka-chan/internal/handler/reward"
 	_ "honoka-chan/internal/handler/scenario"
+	_ "honoka-chan/internal/handler/secretbox"
 	_ "honoka-chan/internal/handler/subscenario"
 	_ "honoka-chan/internal/handler/tos"
 	_ "honoka-chan/internal/handler/unit"