Restructure Dockerfiles and add Oh My Zsh support

Major changes:
- Dockerfile now builds the REMnux-based image (was Dockerfile.remnux)
- Removed redundant Dockerfile.remnux
- Dockerfile.scratch builds from Ubuntu 20.04 (from scratch variant)
- Updated Makefile to reflect new structure:
  - 'make build' for REMnux-based (default)
  - 'make build-scratch' for Ubuntu-based
  - Removed kali references
  - Simplified targets and naming

Zsh improvements:
- Added Oh My Zsh auto-installation on first run
- Pre-install Oh My Zsh in Docker images for remnux user
- Custom prompt with 🔍 indicator for analysis work
- Fallback to minimal config for system users
- Includes plugins: git, docker, command-not-found, colored-man-pages
- Welcome message shows only once per session
- No more first-time configuration prompts

Shell experience:
- bash (default) - traditional, reliable
- zsh - now with Oh My Zsh, custom theme, plugins
- fish - friendly interactive shell

All shells include help aliases and analysis shortcuts.

Makefile

@@ -5,88 +5,75 @@ help:
 	@echo "File Analysis Container - Build System"
 	@echo ""
 	@echo "Available targets:"
-	@echo "  build-upstream    Build from REMnux upstream image (recommended)"
+	@echo "  build             Build from REMnux upstream image (recommended, default)"
 	@echo "  build-scratch     Build from Ubuntu 20.04 base (full control)"
-	@echo "  build-kali        Build from Kali Linux base (legacy)"
 	@echo "  build-all         Build all variants"
 	@echo "  test              Run tests on all builds"
-	@echo "  test-upstream     Test upstream build"
+	@echo "  test-remnux       Test REMnux build"
 	@echo "  test-scratch      Test scratch build"
-	@echo "  test-kali         Test Kali build"
 	@echo "  push              Push images to Docker Hub"
 	@echo "  clean             Remove all built images"
+	@echo "  shell             Interactive shell (REMnux build)"
+	@echo "  shell-scratch     Interactive shell (scratch build)"
+	@echo "  coverage          Check help coverage"
 	@echo ""
 
 # Build targets
-build-upstream:
-	@echo "Building REMnux upstream variant..."
-	docker build -f Dockerfile.remnux -t tabledevil/file-analysis:remnux .
-	@echo "✓ Build complete: tabledevil/file-analysis:remnux"
+build:
+	@echo "Building REMnux-based file analysis container..."
+	docker build -t tabledevil/file-analysis:latest .
+	docker tag tabledevil/file-analysis:latest tabledevil/file-analysis:remnux
+	@echo "✓ Build complete: tabledevil/file-analysis:latest"
 
 build-scratch:
 	@echo "Building from scratch (Ubuntu 20.04 base)..."
 	docker build -f Dockerfile.scratch -t tabledevil/file-analysis:scratch .
 	@echo "✓ Build complete: tabledevil/file-analysis:scratch"
 
-build-kali:
-	@echo "Building Kali Linux variant..."
-	docker build -f Dockerfile -t tabledevil/file-analysis:kali .
-	@echo "✓ Build complete: tabledevil/file-analysis:kali"
-
-build-all: build-upstream build-scratch build-kali
+build-all: build build-scratch
 	@echo "✓ All variants built successfully"
 
 # Test targets
-test: test-upstream test-scratch test-kali
+test: test-remnux test-scratch
 	@echo "✓ All tests passed"
 
-test-upstream:
-	@echo "Testing REMnux upstream build..."
-	@docker run --rm tabledevil/file-analysis:remnux bash -c "which fhelp && fhelp cheat pdfid"
-	@docker run --rm tabledevil/file-analysis:remnux bash -c "which pdfid.py && which capa && which visidata"
-	@echo "✓ Upstream build tests passed"
+test-remnux:
+	@echo "Testing REMnux build..."
+	@docker run --rm tabledevil/file-analysis:latest bash -c "which fhelp && fhelp cheat pdfid"
+	@docker run --rm tabledevil/file-analysis:latest bash -c "which pdfid.py && which capa && which visidata"
+	@docker run --rm tabledevil/file-analysis:latest bash -c "zsh --version && fish --version"
+	@echo "✓ REMnux build tests passed"
 
 test-scratch:
 	@echo "Testing scratch build..."
 	@docker run --rm tabledevil/file-analysis:scratch bash -c "which fhelp && fhelp cheat pdfid"
-	@docker run --rm tabledevil/file-analysis:scratch bash -c "which pdfid.py && which capa"
+	@docker run --rm tabledevil/file-analysis:scratch bash -c "which pdfid.py && which capa && which pwsh"
+	@docker run --rm tabledevil/file-analysis:scratch bash -c "zsh --version && fish --version"
 	@echo "✓ Scratch build tests passed"
 
-test-kali:
-	@echo "Testing Kali build..."
-	@docker run --rm tabledevil/file-analysis:kali bash -c "which pdfid.py && which capa"
-	@docker run --rm tabledevil/file-analysis:kali bash -c "which pwsh"
-	@echo "✓ Kali build tests passed"
-
 # Docker Hub push
 push:
 	@echo "Pushing images to Docker Hub..."
+	docker push tabledevil/file-analysis:latest
 	docker push tabledevil/file-analysis:remnux
 	docker push tabledevil/file-analysis:scratch
-	docker push tabledevil/file-analysis:kali
-	docker tag tabledevil/file-analysis:remnux tabledevil/file-analysis:latest
-	docker push tabledevil/file-analysis:latest
 	@echo "✓ Images pushed successfully"
 
 # Clean up
 clean:
 	@echo "Removing built images..."
+	-docker rmi tabledevil/file-analysis:latest
 	-docker rmi tabledevil/file-analysis:remnux
 	-docker rmi tabledevil/file-analysis:scratch
-	-docker rmi tabledevil/file-analysis:kali
-	-docker rmi tabledevil/file-analysis:latest
 	@echo "✓ Cleanup complete"
 
 # Interactive shells for testing
-shell-upstream:
-	docker run -it --rm -v "$$(pwd):/data" tabledevil/file-analysis:remnux
+shell:
+	docker run -it --rm -v "$$(pwd):/data" tabledevil/file-analysis:latest
 
 shell-scratch:
 	docker run -it --rm -v "$$(pwd):/data" tabledevil/file-analysis:scratch
 
-shell-kali:
-	docker run -it --rm -v "$$(pwd):/data" tabledevil/file-analysis:kali
-
 # Run help coverage check
 coverage:
 	@echo "Checking help coverage..."