Fix NULL check issues (HIGH priority)

Added validation checks for potentially empty variables before use
to prevent errors and unsafe operations.

WordPress Cron Manager (5 fixes):
- Added site_path validation after dirname operations
- Prevents using empty paths in cd commands and file operations
- Pattern: Check [ -z "$site_path" ] before use

Bot Analyzer:
- Quoted TEMP_DIR in trap command for safety

Hardware Health Check:
- Quoted MESSAGES_CACHE in trap command for safety

Note: 5 issues flagged in toolkit-qa-check.sh were false positives
(echo statements demonstrating bad patterns, not actual code issues)

modules/security/bot-analyzer.sh

@@ -240,7 +240,7 @@ mkdir -p "$TEMP_DIR" || {
 }
 
 # Cleanup on exit
-trap "rm -rf $TEMP_DIR" EXIT
+trap "rm -rf \"$TEMP_DIR\"" EXIT
 
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 # Bot Signature Database