FIX: Automatic OPcache memory calculation within safe limits

Now OPcache memory is automatically calculated to fit within the 60%
RAM safety threshold:

1. PHP-FPM capacity validation now reserves 256MB for OPcache
   - max_safe_php_fpm = (60% RAM) - 256MB
   - Prevents PHP-FPM+OPcache from exceeding safe limits

2. OPcache memory calculation now dynamic:
   - Accepts optional available_memory parameter
   - Won't exceed available limits
   - Minimum 32MB, maximum 256MB (typical servers)

3. Level 5 (Optimize Everything):
   - Calculates available memory after PHP-FPM allocation
   - Passes available memory to OPcache calculation
   - OPcache automatically scales down on low-memory servers

Result: Option 5 now automatically balances PHP-FPM + OPcache
within safe limits without manual configuration.

modules/performance/php-optimizer.sh

@@ -1223,8 +1223,9 @@ is_opcache_enabled() {
 # Calculate optimal OPcache memory
 calculate_optimal_opcache_memory() {
     local avg_rpm="$1"
+    local available_memory="${2:-}"  # Optional: available memory limit
 
-    # Base recommendation in MB
+    # Base recommendation in MB based on traffic
     local memory="64"
 
     if [ "$avg_rpm" -ge 100 ]; then
@@ -1237,6 +1238,17 @@ calculate_optimal_opcache_memory() {
         memory="64"
     fi
 
+    # If available memory is specified, don't exceed it
+    if [ -n "$available_memory" ] && [ "$available_memory" -gt 0 ]; then
+        # Extract numeric value (remove 'M' if present)
+        local avail_num=${available_memory%M}
+        if [ "$memory" -gt "$avail_num" ]; then
+            memory=$avail_num
+        fi
+        # Minimum 32MB for OPcache
+        [ "$memory" -lt 32 ] && memory=32
+    fi
+
     echo "${memory}M"
 }
 
@@ -2527,11 +2539,12 @@ optimize_level_4_opcache() {
 
                 # Enable OPcache
                 if enable_opcache "$ini_file" >/dev/null 2>&1; then
-                    # Calculate optimal memory for OPcache
+                    # Calculate optimal memory for OPcache (safe limit: 256MB max)
                     local avg_rpm
                     avg_rpm=$(calculate_avg_requests_per_minute "$username" 24 | cut -d'|' -f1)
                     local optimal_memory
-                    optimal_memory=$(calculate_optimal_opcache_memory "$avg_rpm")
+                    # Pass 256MB as max available (OPcache is global and shared across all domains)
+                    optimal_memory=$(calculate_optimal_opcache_memory "$avg_rpm" "256")
 
                     # Set memory_consumption
                     if modify_php_ini_setting "$ini_file" "opcache.memory_consumption" "$optimal_memory" >/dev/null 2>&1; then
@@ -2783,7 +2796,9 @@ optimize_level_5_everything() {
     done
 
     # Determine if recommendations are safe
-    local max_safe_php_fpm=$((total_ram_mb * 60 / 100))  # 60% of RAM for PHP-FPM
+    # Reserve up to 256MB for OPcache (will be allocated separately)
+    local max_opcache_reserved=256
+    local max_safe_php_fpm=$((total_ram_mb * 60 / 100 - max_opcache_reserved))  # 60% of RAM minus OPcache reserve
 
     if [ "$total_recommended_memory" -gt "$max_safe_php_fpm" ]; then
         cecho "${RED}${BOLD}⚠ WARNING: Combined recommendations exceed safe limits!${NC}"
@@ -2892,8 +2907,11 @@ optimize_level_5_everything() {
                     if enable_opcache "$ini_file" >/dev/null 2>&1; then
                         local avg_rpm
                         avg_rpm=$(calculate_avg_requests_per_minute "$username" 24 | cut -d'|' -f1)
+                        # Calculate available memory for OPcache (remaining from 60% allocation minus PHP-FPM needs)
+                        local available_for_opcache=$((total_ram_mb * 60 / 100 - total_recommended_memory))
+                        [ "$available_for_opcache" -lt 32 ] && available_for_opcache=32
                         local optimal_opcache_mem
-                        optimal_opcache_mem=$(calculate_optimal_opcache_memory "$avg_rpm")
+                        optimal_opcache_mem=$(calculate_optimal_opcache_memory "$avg_rpm" "$available_for_opcache")
 
                         modify_php_ini_setting "$ini_file" "opcache.memory_consumption" "$optimal_opcache_mem" >/dev/null 2>&1