fix(view): move the ③ colour control into the 3D viewer window

The colour basis control and legend sit below the 3D canvas and show only on ③, so they belong to the model window.

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

index.html

@@ -74,6 +74,13 @@
             <span id="origin" class="muted"></span>
           </div>
           <div id="canvas" class="canvas" aria-label="교각 3D 뷰"></div>
+          <div class="rebar-color" id="rebar-color" hidden role="group" aria-label="철근 색 기준">
+            <span class="lbl">색 기준</span>
+            <button type="button" data-color="role" aria-pressed="true">역할</button>
+            <button type="button" data-color="diameter" aria-pressed="false">직경</button>
+            <button type="button" data-color="member" aria-pressed="false">부재</button>
+            <ul id="rebar-legend" class="rebar-legend"></ul>
+          </div>
           <fieldset class="parts">
             <legend>부재 표시</legend>
             <div id="parts"></div>
@@ -152,13 +159,6 @@
           <p class="pnote">형상은 ② 형상계획 기준입니다. 형상이 바뀌면 "형상 바뀜"으로 표시합니다.</p>
         </aside>
         <div class="center-col">
-          <div class="rebar-color" id="rebar-color" role="group" aria-label="철근 색 기준">
-            <span class="lbl">색 기준</span>
-            <button type="button" data-color="role" aria-pressed="true">역할</button>
-            <button type="button" data-color="diameter" aria-pressed="false">직경</button>
-            <button type="button" data-color="member" aria-pressed="false">부재</button>
-            <ul id="rebar-legend" class="rebar-legend"></ul>
-          </div>
           <div class="viewer-slot" id="slot-rebar"></div>
         <section class="panel viewer" aria-labelledby="rebar-title">
           <div class="viewer-head"><h2 id="rebar-title">철근표</h2></div>