CRITICAL: Fix SYS_* variable reset bug in system-detect.sh

Problem:
- Lines 16-24 reset ALL SYS_* variables to empty EVERY time system-detect.sh is sourced
- When php-analyzer.sh sources system-detect.sh again, it wipes out SYS_CONTROL_PANEL
- Result: get_user_domains() returns empty because SYS_CONTROL_PANEL is empty
- This broke ALL multi-file sourcing scenarios

Root cause:
- export SYS_CONTROL_PANEL="" runs unconditionally on every source
- Multiple libraries source system-detect.sh (user-manager, php-detector, php-analyzer)
- Second sourcing wipes first initialization

Fix:
- Wrap variable initialization in SYS_DETECTION_COMPLETE check
- Variables only reset if detection hasn't run yet
- Preserves values across multiple sourcings

Impact:
- Memory capacity analysis now works (was showing 0 pools)
- All domain iteration works correctly
- Any script that sources multiple libraries now works

lib/system-detect.sh

@@ -12,7 +12,8 @@ if [ -z "$TOOLKIT_BASE_DIR" ]; then
     source "$SCRIPT_DIR/common-functions.sh"
 fi
 
-# Global variables (session-only)
+# Global variables (session-only) - only initialize if not already set
+if [ -z "$SYS_DETECTION_COMPLETE" ]; then
     export SYS_CONTROL_PANEL=""
     export SYS_CONTROL_PANEL_VERSION=""
     export SYS_OS_TYPE=""
@@ -22,6 +23,7 @@ export SYS_WEB_SERVER_VERSION=""
     export SYS_DB_TYPE=""
     export SYS_DB_VERSION=""
     export SYS_LOG_DIR=""
+fi
 export SYS_USER_HOME_BASE=""
 export SYS_PHP_VERSIONS=()
 export SYS_CLOUDFLARE_ACTIVE=""