Add KC target test button, API docs header link, and UI polish

- Add POST /api/v1/picture-targets/{target_id}/test endpoint for single-frame
  color extraction preview on Key Colors targets
- Add test button on KC target cards that opens lightbox with spinner,
  displays captured frame with rectangle overlays and color swatches
- Add API docs link in WebUI header
- Swap confirm dialog button colors (No=red, Yes=neutral)
- Remove type badges from WLED and KC target cards

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/index.html

@@ -16,6 +16,7 @@
                 <span id="server-version"><span id="version-number"></span></span>
             </div>
             <div class="server-info">
+                <a href="/docs" target="_blank" class="header-link" data-i18n-title="app.api_docs" title="API Docs">API</a>
                 <button class="theme-toggle" onclick="toggleTheme()" data-i18n-title="theme.toggle" title="Toggle theme">
                     <span id="theme-icon">🌙</span>
                 </button>
@@ -515,8 +516,8 @@
                 <p id="confirm-message" class="modal-description"></p>
             </div>
             <div class="modal-footer">
-                <button class="btn btn-secondary" id="confirm-no-btn" onclick="closeConfirmModal(false)">No</button>
-                <button class="btn btn-danger" id="confirm-yes-btn" onclick="closeConfirmModal(true)">Yes</button>
+                <button class="btn btn-danger" id="confirm-no-btn" onclick="closeConfirmModal(false)">No</button>
+                <button class="btn btn-secondary" id="confirm-yes-btn" onclick="closeConfirmModal(true)">Yes</button>
             </div>
         </div>
     </div>