perf(booth): optimize assets and result flow

WebP reduces UI payload; JPEG keeps portrait saves compatible.\nFinish ends the visit without prompting another portrait.

lib/config.ts

@@ -47,7 +47,7 @@ const defaultConfig: BoothConfig = {
     accentColor: "#06b6d4",
     surfaceColor: "#170f29",
     textColor: "#ffffff",
-    logoUrl: "/assets/brand/shanghai_karate_logo.png",
+    logoUrl: "/assets/brand/shanghai_karate_logo.webp",
     logoWidth: 260,
   },
   camera: {
@@ -164,20 +164,20 @@ const defaultConfig: BoothConfig = {
       zh: "扫码保存至手机相册",
     },
     downloadLabel: {
-      en: "Save Portrait",
-      zh: "保存高清照",
+      en: "Save",
+      zh: "保存",
     },
     wechatSaveTip: {
-      en: "In WeChat: Long press photo above to save directly!",
-      zh: "微信提示：长按上方图片即可直接保存到相册！",
+      en: "In WeChat, long-press the photo to save it.",
+      zh: "微信中长按照片即可保存。",
     },
     printLabel: {
       en: "Print Photo",
       zh: "打印照片",
     },
     startOverLabel: {
-      en: "Train Again (Start Over)",
-      zh: "再拍一张",
+      en: "Finish",
+      zh: "完成",
     },
     instagramShareLabel: {
       en: "Share Photo",