fix(view): put the ③ colour control in the 3D title row, centred

The colour basis control sits in the 교각 3D 뷰 title row between the 시점 buttons and the origin note.

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

index.html

@@ -71,16 +71,16 @@
           <div class="viewer-head">
             <h2 id="viewer-title">교각 3D 뷰</h2>
             <div id="views" class="views" role="group" aria-label="시점"></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>
             <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>

src/style.css

@@ -706,3 +706,4 @@ body { background: #eef1f4; font-family: 'Noto Sans KR', system-ui, sans-serif;
 .rebar-legend-item { display: flex; align-items: center; gap: 6px; }
 .rebar-legend .swatch { display: inline-block; width: 14px; height: 14px; border-radius: 3px; }
 .rebar-color[hidden] { display: none; }
+.viewer-head .rebar-color { margin: 0 auto; }