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)

test-tmpfs-detection.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# Test script to verify tmpfs/overlay detection functionality
+# Test script to verify tmpfs detection functionality
 # This script can be run without root to test the detection logic
 
 set -euo pipefail
@@ -22,7 +22,7 @@ warn() {
     echo -e "${YELLOW}[INFO]${NC} $1"
 }
 
-echo "🔍 Testing tmpfs/overlay Detection Functionality"
+echo "🔍 Testing tmpfs Detection Functionality"
 echo "=============================================="
 echo ""