Fix Makefile coverage target and add check-help-coverage.sh to containers

- Fixed 'make coverage' command (was using empty variable)
- Now runs: docker run --rm tabledevil/file-analysis:latest check-help-coverage.sh
- Added check-help-coverage.sh script to both Dockerfiles
- Made script executable in both images
- Coverage check now works properly without mounting volumes

Makefile

@@ -77,4 +77,4 @@ shell-scratch:
 # Run help coverage check
 coverage:
 	@echo "Checking help coverage..."
-	docker run --rm tabledevil/file-analysis:remnux check-help-coverage.sh
+	docker run --rm tabledevil/file-analysis:latest check-help-coverage.sh