feat: staggered star reveal and near-miss progress ring

Stars on win now appear sequentially with elastic-bounce via
TweenAnimationBuilder (400/650/900 ms). Lost overlay shows a
CircularProgressIndicator ring with "87% complete!" (l10n:
almostThere) when objectiveProgress > 0.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/l10n/app_en.arb

@@ -20,5 +20,13 @@
         "type": "int"
       }
     }
+  },
+  "almostThere": "{percent}% complete!",
+  "@almostThere": {
+    "placeholders": {
+      "percent": {
+        "type": "int"
+      }
+    }
   }
 }

lib/l10n/app_ko.arb

@@ -13,5 +13,6 @@
   "giveUp": "포기하기",
   "playAgain": "다시 하기",
   "nextStage": "다음 스테이지",
-  "streakMilestone": "{days}일 연속 플레이! 대단해요!"
+  "streakMilestone": "{days}일 연속 플레이! 대단해요!",
+  "almostThere": "{percent}% 달성!"
 }