Perf: Add batch transaction support for search index building

The search index build was extremely slow (25 v/s) due to individual INSERT
statements without transactions. This refactors to use batch inserts with
SQLite transactions, which should increase speed by 100-1000x.

Changes:
- Add insertVersesBatch() method in searchDatabase.js
- Use BEGIN TRANSACTION / COMMIT for batch operations
- Collect all verses for a version, then insert in one transaction
- Removed per-verse insert calls from buildSearchIndex.js
- Batch insert ~31,000 verses per version in single transaction

Expected performance improvement:
- Before: 25 verses/second (~82 minutes for 124k verses)
- After: 2,000-5,000 verses/second (~30-60 seconds for 124k verses)

SQLite is optimized for batched transactions - this is the standard pattern
for bulk data loading.

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

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

backend/src/searchDatabase.js

@@ -113,6 +113,38 @@ class SearchDatabase {
     });
   }
 
+  // Batch insert verses (MUCH faster - uses transactions)
+  async insertVersesBatch(verses) {
+    return new Promise((resolve, reject) => {
+      this.db.serialize(() => {
+        this.db.run('BEGIN TRANSACTION');
+
+        const stmtVerses = this.db.prepare(
+          `INSERT OR IGNORE INTO verses (book, chapter, verse_number, verse_text, version)
+           VALUES (?, ?, ?, ?, ?)`
+        );
+
+        const stmtFts = this.db.prepare(
+          `INSERT INTO verses_fts (book, chapter, verse_number, verse_text, version)
+           VALUES (?, ?, ?, ?, ?)`
+        );
+
+        for (const verse of verses) {
+          stmtVerses.run(verse.book, verse.chapter, verse.verse, verse.text, verse.version);
+          stmtFts.run(verse.book, verse.chapter, verse.verse, verse.text, verse.version);
+        }
+
+        stmtVerses.finalize();
+        stmtFts.finalize();
+
+        this.db.run('COMMIT', (err) => {
+          if (err) reject(err);
+          else resolve();
+        });
+      });
+    });
+  }
+
   // Search using FTS5 with advanced features
   async search(query, options = {}) {
     const {