Refactor search modes and optimize embedding generation

- Updated the dashboard template to hide the Code Graph Explorer feature.
- Enhanced the `executeCodexLens` function to use `exec` for better cross-platform compatibility and improved command execution.
- Changed the default `maxResults` and `limit` parameters in the smart search tool to 10 for better performance.
- Introduced a new `priority` search mode in the smart search tool, replacing the previous `parallel` mode, which now follows a fallback strategy: hybrid -> exact -> ripgrep.
- Optimized the embedding generation process in the embedding manager by batching operations and using a cached embedder instance to reduce model loading overhead.
- Implemented a thread-safe singleton pattern for the embedder to improve performance across multiple searches.

ccw/src/templates/dashboard-js/views/cli-manager.js

@@ -392,7 +392,8 @@ function renderToolsSection() {
     '<div class="tool-item-right">' +
       (codexLensStatus.ready
         ? '<span class="tool-status-text success"><i data-lucide="check-circle" class="w-3.5 h-3.5"></i> v' + (codexLensStatus.version || 'installed') + '</span>' +
-          '<button class="btn-sm btn-outline" onclick="event.stopPropagation(); initCodexLensIndex()"><i data-lucide="database" class="w-3 h-3"></i> ' + t('cli.initIndex') + '</button>' +
+          '<button class="btn-sm btn-outline" onclick="event.stopPropagation(); initCodexLensIndex(\'vector\')" title="' + (t('index.vectorDesc') || 'Semantic search with embeddings') + '"><i data-lucide="sparkles" class="w-3 h-3"></i> ' + (t('index.vectorIndex') || 'Vector') + '</button>' +
+          '<button class="btn-sm btn-outline" onclick="event.stopPropagation(); initCodexLensIndex(\'normal\')" title="' + (t('index.normalDesc') || 'Fast full-text search only') + '"><i data-lucide="file-text" class="w-3 h-3"></i> ' + (t('index.normalIndex') || 'FTS') + '</button>' +
           '<button class="btn-sm btn-outline btn-danger" onclick="event.stopPropagation(); uninstallCodexLens()"><i data-lucide="trash-2" class="w-3 h-3"></i> ' + t('cli.uninstall') + '</button>'
         : '<span class="tool-status-text muted"><i data-lucide="circle-dashed" class="w-3.5 h-3.5"></i> ' + t('cli.notInstalled') + '</span>' +
           '<button class="btn-sm btn-primary" onclick="event.stopPropagation(); installCodexLens()"><i data-lucide="download" class="w-3 h-3"></i> ' + t('cli.install') + '</button>') +