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>

api.asp

@@ -1,21 +1,13 @@
 <%@ Language=VBScript %>
+<!--#include file="includes/config.asp"-->
 <%
 ' ============================================================================
-' DATABASE CONNECTION - Created directly in api.asp to avoid scoping issues
+' DATABASE CONNECTION - Uses centralized config.asp
 ' ============================================================================
-Dim objConn, rs, DB_CONN_STRING
-' Use direct MySQL ODBC driver connection (same as sql.asp) instead of DSN
-DB_CONN_STRING = "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 = 15
+Dim objConn, rs
+Session.Timeout = APP_SESSION_TIMEOUT
 Set objConn = Server.CreateObject("ADODB.Connection")
-objConn.ConnectionString = DB_CONN_STRING
+objConn.ConnectionString = GetConnectionString()
 objConn.Open
 Set rs = Server.CreateObject("ADODB.Recordset")