feat(view): 형상계획 ② screen skeleton with five members (plan.md C1)

- ① and ② are switched from the stage nav. ② shows the pier list with change
  counts, the five members (교량받침, 코핑, 기둥, 확대기초·말뚝, 지반·지층) with
  a change count each, a member card, and a change list with per-item revert.
- The member card shows 기본 and 선택 summaries separately. Only members with
  existing inputs get fields (코핑 폭·길이, 말뚝 길이); the others show values
  and a note that their inputs come in a later step. Unselected members' inputs
  are not shown.
- The field rows are shared between ① and ②.
- Added a global [hidden] rule so hidden screens stay hidden.
- Not verified in a browser.

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

index.html

@@ -14,8 +14,8 @@
           <span id="project-line" class="proj">프로젝트 미지정</span>
         </div>
         <nav class="steps" aria-label="단계">
-          <span class="step current" aria-current="step">① 형상 생성 <em id="step1-status">미생성</em></span>
-          <span class="step" aria-disabled="true">② 형상계획 <em id="step2-status">예정</em></span>
+          <button id="nav-shape" class="step current" type="button" aria-current="step">① 형상 생성 <em id="step1-status">미생성</em></button>
+          <button id="nav-plan" class="step" type="button">② 형상계획 <em id="step2-status">예정</em></button>
           <span class="step" aria-disabled="true">③ 철근배근 <em>예정</em></span>
         </nav>
         <div class="actions">
@@ -35,7 +35,7 @@
         <button id="discard-backup" class="btn small" type="button">버리기</button>
       </div>
 
-      <main class="grid">
+      <main class="grid" id="view-shape">
         <aside class="panel piers" aria-labelledby="pier-title">
           <p id="pier-title" class="lbl">교각 목록</p>
           <div class="pier-tools">
@@ -106,6 +106,33 @@
         </aside>
       </main>
 
+      <main class="grid plan" id="view-plan" hidden>
+        <aside class="panel piers" aria-labelledby="plan-pier-title">
+          <p id="plan-pier-title" class="lbl">교각 목록</p>
+          <div class="phead" aria-hidden="true"><span></span><span>교각</span><span>변경</span></div>
+          <ul id="plan-pier-items" class="pier-items"></ul>
+          <p class="lbl members-title">부재 · 5개</p>
+          <ul id="members" class="members"></ul>
+        </aside>
+
+        <section class="panel viewer" aria-labelledby="member-title">
+          <div class="viewer-head">
+            <h2 id="member-title">코핑</h2>
+          </div>
+          <p id="member-summary" class="num"></p>
+          <div id="member-fields"></div>
+          <p id="member-note" class="muted small"></p>
+          <button id="member-regen" class="btn primary" type="button" disabled>다시 생성 · 변경 0</button>
+        </section>
+
+        <aside class="panel results" aria-labelledby="changes-title">
+          <h2 id="changes-title">기본값 대비 변경</h2>
+          <ul id="changes" class="issues"></ul>
+          <h2>알림</h2>
+          <ul id="plan-issues" class="issues"></ul>
+        </aside>
+      </main>
+
     </div>
 
     <dialog id="import-dialog" aria-labelledby="dlg-title">