Fix final 3 HIGH integer comparisons - ALL HIGH ISSUES RESOLVED!

FIXES:
acronis-logs.sh:
- Line 278: $choice → ${choice:-0} (2 instances)

acronis-register.sh:
- Line 174: $REG_EXIT_CODE → ${REG_EXIT_CODE:-0}

acronis-uninstall.sh:
- Line 217: $remaining → ${remaining:-0}

MILESTONE ACHIEVED:
🎉 ALL HIGH-PRIORITY INTEGER COMPARISON ISSUES FIXED! 🎉

QA STATUS:
- CRITICAL issues: 0 (was 8)  ✓ FIXED
- HIGH issues: 0 (was 20+)    ✓ FIXED
- MEDIUM issues: 9            (pending)
- LOW issues: 11              (pending)
- Total issues: 20 (was 41 originally)

STATISTICS:
- Files fixed: 25+
- Integer comparisons fixed: 60+
- Commits in this session: 6
- All critical bash errors eliminated!

Remaining work:
- 9 MEDIUM: Hardcoded /var/cpanel paths (multi-panel support)
- 11 LOW: bc command usage + undefined color variable

modules/backup/acronis-logs.sh

@@ -275,7 +275,7 @@ while true; do
             # Check if numeric selection for specific log file
             if [[ "$choice" =~ ^[0-9]+$ ]]; then
                 log_files=($(find "$LOG_DIR" -name "*.log" -type f | sort))
-                if [ $choice -gt 0 ] && [ $choice -le ${#log_files[@]} ]; then
+                if [ "${choice:-0}" -gt 0 ] && [ "${choice:-0}" -le ${#log_files[@]} ]; then
                     selected_log="${log_files[$((choice-1))]}"
                     clear
                     print_banner "Log: $(basename "$selected_log")"