fix: 달력 레이아웃 1.3.0 버전처럼 복원

- 양쪽 마진 4dp → 12dp 복원
- 달력 아이템 높이 92dp 고정으로 복원
- shiftChar 크기 48dp → 40dp 복원
- 달력 화면이 ConstraintLayout에 자연스럽게 채워지도록 수정

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

app/src/main/res/layout/activity_main.xml

@@ -58,12 +58,12 @@
 
     </androidx.constraintlayout.widget.ConstraintLayout>
 
-    <!-- Maximized Calendar Card - Reduced margins for wider calendar -->
+    <!-- Maximized Calendar Card -->
     <androidx.cardview.widget.CardView
         android:id="@+id/calendarCard"
         android:layout_width="0dp"
         android:layout_height="0dp"
-        android:layout_marginHorizontal="4dp"
+        android:layout_marginHorizontal="12dp"
         android:layout_marginBottom="8dp"
         app:cardCornerRadius="28dp"
         app:cardElevation="0dp"
@@ -240,7 +240,7 @@
         android:id="@+id/otherTeamsCard"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        android:layout_marginHorizontal="4dp"
+        android:layout_marginHorizontal="12dp"
         android:layout_marginBottom="16dp"
         app:cardCornerRadius="20dp"
         app:cardElevation="0dp"