Fix SCRIPT_DIR variable collision preventing PHP optimizer from running

CRITICAL BUG FIX:
- PHP optimizer failed with 'php-config-manager.sh not found' error
- Root cause: Multiple sourced libraries redefining SCRIPT_DIR variable
- Sourcing chain: php-optimizer → php-detector → system-detect + user-manager
- Each library was overwriting parent's SCRIPT_DIR causing /lib/lib/ double paths

CHANGES:
- php-optimizer.sh: Renamed SCRIPT_DIR → PHP_TOOLKIT_DIR (unique variable)
- user-manager.sh: Renamed SCRIPT_DIR → _LIB_SRCDIR to avoid collision
- php-optimizer.sh: Fixed detect_system() → initialize_system_detection()
- Removed 2>/dev/null error suppression to see actual errors during debug

RESULT:
- Script now loads all libraries successfully
- Menu displays correctly with all 9 options
- System detection runs properly
- Ready for testing

Files modified:
- lib/user-manager.sh (3 lines)
- modules/performance/php-optimizer.sh (10 lines)

lib/user-manager.sh

@@ -7,9 +7,9 @@
 
 # Source dependencies
 if [ -z "$TOOLKIT_BASE_DIR" ]; then
-    SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-    source "$SCRIPT_DIR/common-functions.sh"
-    source "$SCRIPT_DIR/system-detect.sh"
+    _LIB_SRCDIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+    source "$_LIB_SRCDIR/common-functions.sh"
+    source "$_LIB_SRCDIR/system-detect.sh"
 fi
 
 # Initialize temp session directory if not set