fix: remove unused nodes-v2.db and update database paths

- Removed unused empty nodes-v2.db file
- Updated NodeDocumentationService to use nodes.db as default
- Updated test file to use correct database
- Added secret scanning exclusion for database files

This prevents confusion about which database is actually used and removes
the file that GitHub's security advisor was flagging.

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

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

tests/test-node-documentation-service.js

@@ -5,8 +5,8 @@ const { NodeDocumentationService } = require('../dist/services/node-documentatio
 async function testService() {
   console.log('=== Testing Node Documentation Service ===\n');
   
-  // Use a separate database for v2
-  const service = new NodeDocumentationService('./data/nodes-v2.db');
+  // Use the main database
+  const service = new NodeDocumentationService('./data/nodes.db');
   
   try {
     // Test 1: List nodes