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/sql.asp

@@ -1,18 +1,9 @@
+<!--#include file="config.asp"-->
 <%
 	' objConn - script-global connection object (no Dim for global scope)
-	Session.Timeout=15
-	Set objConn=Server.CreateObject("ADODB.Connection")
-	' Old DSN connection:
-	' objConn.ConnectionString="DSN=shopdb;Uid=root;Pwd=WJF11sql"
-	' Direct MySQL ODBC connection with pooling enabled:
-	objConn.ConnectionString="Driver={MySQL ODBC 9.4 Unicode Driver};" & _
-	                         "Server=192.168.122.1;" & _
-	                         "Port=3306;" & _
-	                         "Database=shopdb;" & _
-	                         "User=570005354;" & _
-	                         "Password=570005354;" & _
-	                         "Option=3;" & _
-	                         "Pooling=True;Max Pool Size=100;"
+	Session.Timeout = APP_SESSION_TIMEOUT
+	Set objConn = Server.CreateObject("ADODB.Connection")
+	objConn.ConnectionString = GetConnectionString()
 	objConn.Open
-	set rs = server.createobject("ADODB.Recordset")
+	Set rs = Server.CreateObject("ADODB.Recordset")
 %>