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)

CHANGELOG.md

@@ -1,5 +1,26 @@
 # Changelog
 
+## [2025-09-23] - Overlay Filesystem Removal
+
+### Removed
+- **Overlay filesystem functionality**: Removed unused overlay filesystem features
+  - Removed `OVERLAY_ENABLED` and `OVERLAY_PROTECT_CONFIGS` from configuration
+  - Removed `overlayfs` sections from all profile JSON files
+  - Removed overlay references from documentation and scripts
+  - Added overlay detection and removal functionality for existing mounts
+
+### Added
+- **Overlay cleanup functionality**: Added ability to detect and remove overlay mounts
+  - `remove_overlays()` function to safely unmount overlay filesystems
+  - Automatic cleanup of overlay work/upper directories
+  - Removal of overlay entries from /etc/fstab
+  - User prompt when overlay mounts are detected
+
+### Rationale
+- Overlay filesystems are complex and rarely needed on desktop systems
+- Most users benefit more from tmpfs cache optimization than overlay complexity
+- Simplified codebase by removing unused/incomplete functionality
+
 ## [2025-09-23] - tmpfs Setup Fix
 
 ### Fixed