Fix: Remove references to old search engine variables

Removed leftover references to esvSearchEngine, nltSearchEngine, and csbSearchEngine
in the server startup code. These were causing ReferenceError after migration to FTS5.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/src/index.js

@@ -459,16 +459,9 @@ app.use((err, req, res, next) => {
 // Start server
 app.listen(PORT, () => {
   console.log(`The Bible API server running on port ${PORT}`);
-  if (esvSearchEngine) {
   console.log(`ESV data directory: ${ESV_DATA_DIR}`);
-  } else {
-    console.log(`ESV data not available - mdbible not found`);
-  }
   console.log(`NKJV data directory: ${NKJV_DATA_DIR}`);
-  if (nltSearchEngine) {
   console.log(`NLT data directory: ${NLT_DATA_DIR}`);
-  }
-  if (csbSearchEngine) {
   console.log(`CSB data directory: ${CSB_DATA_DIR}`);
-  }
+  console.log('Using FTS5 full-text search (SQLite)');
 });