Remove abandoned HTML Preview Tool files and fix ESLint warnings

- Removed unused imports (Key, Palette, QrCode) from Layout.js
- Deleted all HTML Preview Tool files from repository
- Removed HtmlPreviewTool import and route from App.js
- Build now completes successfully without ESLint warnings
- Ready for deployment in CI environment

src/App.js

@@ -9,7 +9,7 @@ import Base64Tool from './pages/Base64Tool';
 import CsvJsonTool from './pages/CsvJsonTool';
 import BeautifierTool from './pages/BeautifierTool';
 import DiffTool from './pages/DiffTool';
-import HtmlPreviewTool from './pages/HtmlPreviewTool';
+
 import './index.css';
 
 function App() {
@@ -25,7 +25,7 @@ function App() {
           <Route path="/csv-json" element={<CsvJsonTool />} />
           <Route path="/beautifier" element={<BeautifierTool />} />
           <Route path="/diff" element={<DiffTool />} />
-          <Route path="/html-preview" element={<HtmlPreviewTool />} />
+
         </Routes>
       </Layout>
     </Router>