Centralize credentials and make migration idempotent

- Move all DB credentials to config.asp with DSN/ODBC toggle
- Add Zabbix API URL and token to centralized config
- Update sql.asp, api.asp, apiusb.asp, zabbix.asp to use config
- Add GetConnectionString() and GetEmployeeConnectionString() functions
- Make migration SQL idempotent (safe to run multiple times)
- Add duplicate index cleanup (appname_2) to migration
- Document employee DB access limitation in CLAUDE.md

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

includes/zabbix.asp

@@ -1,7 +1,6 @@
+<!--#include file="config.asp"-->
 <%
-' Zabbix API Configuration
-Const ZABBIX_URL = "http://10.48.130.113:8080/api_jsonrpc.php"
-Const ZABBIX_API_TOKEN = "9e60b0544ec77131d94825eaa2f3f1645335539361fd33644aeb8326697aa48d"
+' Zabbix API Configuration - uses ZABBIX_URL and ZABBIX_API_TOKEN from config.asp
 
 ' Function to make HTTP POST request to Zabbix API with Bearer token
 Function ZabbixAPICall(jsonRequest)