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/sql/grants-public.sql

@@ -274,12 +274,22 @@ GRANT SELECT ON CONTAFIN_ORACLE.VDEF_PROGRAME_SERII TO CONTAFIN_ORACLE;
 
 PROMPT [8/9] Granting directory and system permissions...
 
--- Create DMPDIR directory if it doesn't exist (adjust path as needed)
+-- DMPDIR directory should already exist (created by 01-setup-database.ps1)
+-- Only grant permissions here - don't override the path
+-- If DMPDIR doesn't exist, create with standard path C:\DMPDIR
+DECLARE
+    v_count NUMBER;
 BEGIN
-    EXECUTE IMMEDIATE 'CREATE OR REPLACE DIRECTORY DMPDIR AS ''D:\Oracle\admin\ORCL\dpdump''';
+    SELECT COUNT(*) INTO v_count FROM dba_directories WHERE directory_name = 'DMPDIR';
+    IF v_count = 0 THEN
+        EXECUTE IMMEDIATE 'CREATE DIRECTORY DMPDIR AS ''C:\DMPDIR''';
+        DBMS_OUTPUT.PUT_LINE('  Created DMPDIR directory (C:\DMPDIR)');
+    ELSE
+        DBMS_OUTPUT.PUT_LINE('  DMPDIR directory already exists - preserving existing path');
+    END IF;
 EXCEPTION
     WHEN OTHERS THEN
-        DBMS_OUTPUT.PUT_LINE('Note: DMPDIR directory may already exist or path needs adjustment');
+        DBMS_OUTPUT.PUT_LINE('Note: DMPDIR ' || SQLERRM);
 END;
 /