Fix critical bugs found by QA tool: grep -F, integer comparisons, function exports

CRITICAL FIXES (8 → 0):
- Fix all 8 grep -F with regex anchors bugs
  - lib/reference-db.sh:420
  - lib/user-manager.sh:195, 254, 258, 317, 583, 590
  - modules/website/500-error-tracker.sh:313
  - Changed grep -F to grep for proper regex support

HIGH PRIORITY FIXES:
- Add 36 function exports for subshell availability
  - lib/system-detect.sh: 10 functions
  - lib/common-functions.sh: 26 functions

- Fix 27 integer comparisons with ${var:-0} validation
  - lib/common-functions.sh: 7 fixes
  - lib/ip-reputation.sh: 3 fixes
  - lib/user-manager.sh: 4 fixes
  - launcher.sh: 7 fixes
  - modules/website/500-error-tracker.sh: 1 fix
  - modules/performance/hardware-health-check.sh: 2 fixes
  - modules/performance/mysql-query-analyzer.sh: 1 fix
  - modules/security/bot-analyzer.sh: 11 fixes

- Change exit to return in library file
  - lib/common-functions.sh:246 (require_root function)

DOCUMENTATION:
- Add [DEVELOPMENT_WORKFLOW] section to REFDB_FORMAT.txt
  - Document QA script as "third option" for validation
  - Add recommended workflow for using QA tool
  - Document all 16 checks (11 bug + 5 performance)

IMPACT:
- Before: 41 issues (8 CRITICAL + 13 HIGH + 9 MEDIUM + 11 LOW)
- After: 30 issues (0 CRITICAL + 10 HIGH + 9 MEDIUM + 11 LOW)
- 27% reduction, all CRITICAL bugs eliminated

QA Tool: bash /tmp/toolkit-qa-check.sh /root/server-toolkit

lib/common-functions.sh

@@ -207,7 +207,7 @@ format_bytes() {
     local unit=0
     local size=$bytes
 
-    while [ $size -gt 1024 ] && [ $unit -lt 4 ]; do
+    while [ "${size:-0}" -gt 1024 ] && [ "${unit:-0}" -lt 4 ]; do
         size=$((size / 1024))
         unit=$((unit + 1))
     done
@@ -223,11 +223,11 @@ format_duration() {
     local minutes=$(((seconds % 3600) / 60))
     local secs=$((seconds % 60))
 
-    if [ $days -gt 0 ]; then
+    if [ "${days:-0}" -gt 0 ]; then
         echo "${days}d ${hours}h ${minutes}m"
-    elif [ $hours -gt 0 ]; then
+    elif [ "${hours:-0}" -gt 0 ]; then
         echo "${hours}h ${minutes}m ${secs}s"
-    elif [ $minutes -gt 0 ]; then
+    elif [ "${minutes:-0}" -gt 0 ]; then
         echo "${minutes}m ${secs}s"
     else
         echo "${secs}s"
@@ -243,7 +243,7 @@ command_exists() {
 require_root() {
     if [ "$EUID" -ne 0 ]; then
         print_error "This script must be run as root"
-        exit 1
+        return 1
     fi
 }
 
@@ -299,3 +299,31 @@ load_config() {
         source "$config_file"
     fi
 }
+
+# Export all functions for use in subshells and sourced scripts
+export -f print_banner
+export -f print_section
+export -f print_info
+export -f print_success
+export -f print_warning
+export -f print_error
+export -f print_critical
+export -f print_alert
+export -f print_header
+export -f cecho
+export -f press_enter
+export -f show_banner
+export -f show_progress
+export -f finish_progress
+export -f show_terminal_info
+export -f create_temp_session
+export -f confirm
+export -f format_bytes
+export -f format_duration
+export -f command_exists
+export -f require_root
+export -f safe_append
+export -f log_message
+export -f get_script_dir
+export -f get_toolkit_dir
+export -f load_config