Fix DMPDIR handling and datafile auto-detection for ROA Windows setup

- New-OracleDirectory: Improved verification with direct SQL check, preserves
  existing DMPDIR path instead of blindly recreating
- Get-DatafilePath: Better fallback logic using ORACLE_HOME to derive path,
  no longer hardcodes C:\app\oracle
- grants-public.sql: Fixed DMPDIR creation - now preserves existing path
  instead of overriding with wrong D:\Oracle\admin\ORCL\dpdump
- config.example.ps1: Added DATAFILE_DIR parameter with documentation

These fixes ensure scripts work without manual intervention on fresh Oracle XE
installations where default DMPDIR points to non-existent paths.

Tested on VM 302 - full installation (01-08) now completes successfully.

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

proxmox/lxc108-oracle/roa-windows-setup/config.example.ps1

@@ -37,5 +37,13 @@ $COMPANY_PASSWORD = "ROMFASTSOFT"
 # Directory for DMP files (Data Pump import/export)
 $DMPDIR = "C:\DMPDIR"
 
+# Datafile directory for tablespace ROA
+# Auto-detected from database if not set. Set this if auto-detection fails.
+# Common paths:
+#   XE 21c: C:\app\<user>\product\21c\oradata\XE\XEPDB1
+#   SE 21c: C:\app\<user>\oradata\ROA
+# To find actual path: SELECT file_name FROM dba_data_files WHERE ROWNUM = 1;
+$DATAFILE_DIR = $null  # e.g., "C:\app\romfast\product\21c\oradata\XE\XEPDB1"
+
 # ROAUPDATE base path (for automatic updates module)
 $ROAUPDATE_BASE_PATH = "D:\ROAUPDATE"