Add Oracle 18c sqlnet.ora config for old ODBC/Instant Client 11g compatibility

- Add config/sqlnet.ora with ALLOWED_LOGON_VERSION=8 for old client support
- Add scripts/fix-sqlnet.sh startup script to persist config across container restarts
- Update README with ORA-28040 troubleshooting, ODBC connection params, and deployment instructions
- Fix SID description: Oracle 18c has PDB (XEPDB1), not non-CDB
- Update container recreation instructions with startup scripts volume

Resolves ORA-28040: No matching authentication protocol when connecting
from Windows ODBC with Oracle Instant Client 11.2

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

proxmox/lxc108-oracle/scripts/fix-sqlnet.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+# =============================================================================
+# fix-sqlnet.sh - Startup script pentru Oracle 18c XE
+# =============================================================================
+# Scop: Restaurează sqlnet.ora cu suport pentru clienți vechi (Instant Client 11g)
+#       la fiecare pornire a containerului Docker.
+#
+# Locație în container: /opt/oracle/scripts/startup/fix-sqlnet.sh
+# Executat automat de: gvenzl/oracle-xe la pornirea containerului
+#
+# Problema rezolvată: ORA-28040: No matching authentication protocol
+# Cauză: Oracle 18c implicit nu acceptă autentificare de la clienți 11g
+# =============================================================================
+
+CONFIG_SOURCE="/opt/oracle/oradata/dbconfig/sqlnet.ora"
+CONFIG_DEST="/opt/oracle/product/18c/dbhomeXE/network/admin/sqlnet.ora"
+
+if [ -f "$CONFIG_SOURCE" ]; then
+    cp "$CONFIG_SOURCE" "$CONFIG_DEST"
+    echo "[fix-sqlnet.sh] Copied custom sqlnet.ora with old auth protocol support"
+else
+    echo "[fix-sqlnet.sh] WARNING: $CONFIG_SOURCE not found, using default sqlnet.ora"
+fi