Move SEL/GET buttons to view-bar as grouped button pair

- Moved SEL and GET buttons from topbar to view-bar
- Created button group with consistent styling
- Positioned to the left of Grid/Tree/Graph tabs
- Added spacer for balanced layout

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

deck-frontend/index.html

@@ -17,9 +17,6 @@
           <option value="ch">CH</option>
         </select>
         <button class="btn btn-sm" id="btn-api">API</button>
-        <button class="btn btn-sm" id="btn-sel">SEL</button>
-        <span id="sel-count"></span>
-        <button class="btn btn-sm" id="btn-get">GET</button>
       </div>
       <div class="topbar-center">
         <!-- Taxonomía -->
@@ -60,11 +57,17 @@
 
     <!-- VIEW BAR -->
     <div class="view-bar">
+      <div class="sel-group">
+        <button class="sel-btn" id="btn-sel">SEL</button>
+        <button class="sel-btn" id="btn-get">GET</button>
+        <span id="sel-count"></span>
+      </div>
       <div class="view-tabs">
         <button class="view-tab active" data-view="grid">Grid</button>
         <button class="view-tab" data-view="tree">Tree</button>
         <button class="view-tab" data-view="graph">Graph</button>
       </div>
+      <div class="view-bar-spacer"></div>
     </div>
 
     <!-- GROUPS BAR -->