ui: 입고센터 드롭다운 가나다순, 사이드바 hover 개선, 달력 버튼 강조

- 출고 폼 입고센터 드롭다운 이름 오름차순 정렬
- 사이드바: is-active 메뉴는 hover 무변화, 그 외 진한 회색(#d9d9d9)
- 설정/센터/박스 페이지 "← 달력" → "◀◀ 달력", 검정 배경 흰 글씨(primary)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/modules/cupang/router.py

@@ -214,7 +214,7 @@ def _form_context(request: Request, store: Any, user: dict[str, Any]) -> dict[st
         "user": user,
         "is_admin": is_admin(user),
         "nav_items": build_erp_nav(user, active="cupang"),
-        "centers": store.list_centers(),
+        "centers": sorted(store.list_centers(), key=lambda c: c["name"]),
         "box_rules": store.list_box_rules(),
         "products": store.list_products(),
         "ship_methods": list(SHIP_METHODS),

app/modules/cupang/templates/cupang/box_rules.html

@@ -6,7 +6,7 @@
 <section class="cpg">
 
   <div class="erp-page-actions">
-    <a class="erp-btn erp-btn-outline" href="/cupang/">← 달력</a>
+    <a class="erp-btn erp-btn-primary" href="/cupang/">◀◀ 달력</a>
   </div>
 
   <!-- 추가/수정 (product_code UNIQUE → upsert) -->

app/modules/cupang/templates/cupang/centers.html

@@ -6,7 +6,7 @@
 <section class="cpg">
 
   <div class="erp-page-actions">
-    <a class="erp-btn erp-btn-outline" href="/cupang/">← 달력</a>
+    <a class="erp-btn erp-btn-primary" href="/cupang/">◀◀ 달력</a>
   </div>
 
   <!-- 추가 (슬림) -->

app/modules/cupang/templates/cupang/products.html

@@ -6,7 +6,7 @@
 <section class="cpg">
 
   <div class="erp-page-actions">
-    <a class="erp-btn erp-btn-outline" href="/cupang/">← 달력</a>
+    <a class="erp-btn erp-btn-primary" href="/cupang/">◀◀ 달력</a>
   </div>
 
   <div class="cpg-prod-layout">