feat(view): 교각 목록 and bulk line in the ③ left column (시안 ③)

The ③ screen had no pier list. The left column now has the 교각 목록 with
checkboxes and a 배근 status (계산됨 / 오류), the 선택 n기 line with 속성 복사…,
then 부재 · 배근 타입. The checks are shared with ① and ②.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

index.html

@@ -135,8 +135,16 @@
       </main>
 
       <main class="grid rebar" id="view-rebar" hidden>
-        <aside class="panel piers" aria-labelledby="rebar-member-title">
-          <p id="rebar-member-title" class="lbl">부재</p>
+        <aside class="panel piers" aria-labelledby="rebar-pier-title">
+          <p id="rebar-pier-title" class="lbl">교각 목록</p>
+          <div class="phead" aria-hidden="true"><span></span><span>교각</span><span>배근</span></div>
+          <ul id="rebar-pier-items" class="pier-items"></ul>
+          <div class="bulk">
+            <b id="rebar-bulk-count">선택 0기</b>
+            <span class="grow"></span>
+            <button id="rebar-bulk-copy" class="btn-o" type="button" disabled>속성 복사…</button>
+          </div>
+          <p id="rebar-member-title" class="lbl members-title">부재 · 배근 타입</p>
           <ul id="rebar-tabs" class="members"></ul>
           <p class="pnote">형상은 ② 형상계획 기준입니다. 형상이 바뀌면 "형상 바뀜"으로 표시합니다.</p>
         </aside>