Remove overlay filesystem functionality and add detection/removal capability

- Remove unused overlay filesystem configuration and references
- Remove overlayfs sections from all profile JSON files
- Remove OVERLAY_ENABLED/OVERLAY_PROTECT_CONFIGS from config
- Update documentation to focus on tmpfs optimization
- Add overlay detection and removal functionality for cleanup
- Add remove_overlays() function with safe unmounting
- Add overlay status reporting in final optimization summary
- Add test-overlay-detection.sh for testing detection logic
- Simplify codebase by removing complex unused features
- Focus on proven desktop optimizations (tmpfs, zram, kernel)

demo-tmpfs-scan.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# Demonstration script showing tmpfs/overlay detection and setup
+# Demonstration script showing tmpfs detection and setup
 # This script shows what would happen on a fresh system
 
 set -euo pipefail
@@ -27,7 +27,7 @@ error() {
     echo -e "${RED}[WOULD DO]${NC} $1"
 }
 
-echo "🔍 tmpfs/Overlay Detection and Setup Demonstration"
+echo "🔍 tmpfs Detection and Setup Demonstration"
 echo "=================================================="
 echo ""
 
@@ -117,7 +117,7 @@ simulate_fresh_system_scan() {
                 size=$(du -sh "$node_dir" 2>/dev/null | cut -f1)
                 project_path=$(dirname "$node_dir")
                 warn "    Found: $project_path ($size)"
-                error "    → Could create overlay mount for faster access"
+                error "    → Could cache in tmpfs for faster access"
             fi
         done
     fi