Eliminate all bc command dependencies - replace with awk for portability

PROBLEM:
- bc command not installed on all systems (requires bc package)
- 30 instances across toolkit causing potential failures
- bc is external dependency for floating-point arithmetic

SOLUTION:
- Replaced all bc usage with awk (universally available)
- Pattern: echo "X * Y" | bc → awk "BEGIN {printf \"%.2f\", X * Y}"
- Pattern: (( $(echo "X > Y" | bc -l) )) → awk comparison + bash test

FILES MODIFIED (8 files, 30 bc instances eliminated):
1. lib/threat-intelligence.sh (1 fix)
   - Line 310: Load average to integer conversion

2. lib/reference-db.sh (2 fixes)
   - Line 554: CPU load percentage calculation
   - Line 570: TCP retransmission comparison

3. lib/php-analyzer.sh (5 fixes)
   - Line 138: Script duration comparison
   - Lines 391-395: OPcache hit rate + wasted memory + cached scripts
   - Line 479: OPcache hit rate threshold

4. modules/performance/hardware-health-check.sh (1 fix)
   - Line 264: CPU frequency conversion (KHz to GHz)

5. modules/performance/network-bandwidth-analyzer.sh (3 fixes)
   - Line 168: Daily bandwidth threshold (50 GiB)
   - Line 238: Bytes to MB conversion
   - Lines 388-390: TCP retransmission percentage

6. modules/performance/php-optimizer.sh (2 fixes)
   - Lines 457, 653: OPcache hit rate comparisons

7. modules/diagnostics/system-health-check.sh (10 fixes)
   - Lines 345-350: Load per core + threshold calculations
   - Lines 354-358: Load trend detection (3 comparisons)
   - Lines 367-406: Load critical/warning/elevated checks
   - Lines 828-829: TCP retransmission analysis
   - Line 901: Clock offset detection
   - Line 1692: Network stats TCP retrans percent

8. tools/toolkit-qa-check.sh (QA improvements)
   - Added --exclude="toolkit-qa-check.sh" to prevent self-scanning
   - Eliminates false positives from QA script itself

TECHNICAL DETAILS:
- All awk commands use BEGIN block for pure calculation
- printf formatting preserves decimal precision (%.2f, %.1f, %.0f)
- Error handling with 2>/dev/null || echo fallbacks
- Ternary operators for comparisons: (condition ? 1 : 0)

TESTING:
✓ QA scan shows 0 CRITICAL, 0 HIGH, 0 MEDIUM, 0 LOW issues
✓ All 30 bc instances eliminated
✓ No external dependencies beyond standard bash + awk
✓ Toolkit now portable to minimal Linux installations

IMPACT:
+ Eliminates bc package dependency
+ 100% portable (awk included in all Unix/Linux systems)
+ Same accuracy for floating-point calculations
+ Faster execution (awk is typically faster than bc)
+ Better error handling with fallback values

lib/reference-db.sh

@@ -551,7 +551,7 @@ db_is_system_under_load() {
 
     # Consider system under load if CPU > 80% or memory > 90%
     if [ -n "$cpu_load" ] && [ -n "$cpu_cores" ]; then
-        local load_percent=$(echo "scale=0; ($cpu_load / $cpu_cores) * 100" | bc 2>/dev/null || echo "0")
+        local load_percent=$(awk "BEGIN {printf \"%.0f\", ($cpu_load / $cpu_cores) * 100}" 2>/dev/null || echo "0")
         if [ "$load_percent" -gt 80 ] || [ "${mem_percent:-0}" -gt 90 ]; then
             return 0  # True - system is under load
         fi
@@ -567,7 +567,8 @@ db_has_network_issues() {
 
     # Consider network problematic if retrans > 5% or errors > 100
     if [ -n "$tcp_retrans" ]; then
-        if (( $(echo "$tcp_retrans > 5" | bc -l 2>/dev/null || echo 0) )) || \
+        local retrans_high=$(awk "BEGIN {print ($tcp_retrans > 5 ? 1 : 0)}" 2>/dev/null || echo 0)
+        if [ "$retrans_high" -eq 1 ] || \
            [ "${rx_errors:-0}" -gt 100 ] || [ "${tx_errors:-0}" -gt 100 ]; then
             return 0  # True - network has issues
         fi