Add Docker support

- Dockerfile with Python 3.12, git, and optional Qt6 for GUI
- docker-compose.yml with services: cli, build, test-install, gui, shell

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

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+# CascadingDev Simplified - Git-native AI collaboration framework
+#
+# Build: docker build -t cascadingdev .
+# Test:  docker run -it --rm cascadingdev cdev --help
+
+FROM python:3.12-slim
+
+LABEL maintainer="rob"
+LABEL description="CascadingDev - Git hooks and cascading rules framework"
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    git \
+    # Qt6 dependencies for Ramble GUI (optional)
+    libgl1-mesa-glx \
+    libegl1-mesa \
+    libxkbcommon0 \
+    libdbus-1-3 \
+    libxcb-cursor0 \
+    libxcb-icccm4 \
+    libxcb-keysyms1 \
+    libxcb-shape0 \
+    libxcb-xinerama0 \
+    libxcb-randr0 \
+    libxcb-render-util0 \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+# Copy project files
+COPY pyproject.toml VERSION README.md ./
+COPY src/ ./src/
+COPY assets/ ./assets/
+COPY tools/ ./tools/
+COPY docs/ ./docs/
+
+# Install CascadingDev
+RUN pip install --no-cache-dir -e .
+
+# Install PySide6 for Ramble GUI (optional, makes image larger)
+RUN pip install --no-cache-dir PySide6 || true
+
+# Verify installation
+RUN cdev --help
+
+# Default: show help
+CMD ["cdev", "--help"]
+
+# ==============================================================================
+# Usage Examples
+# ==============================================================================
+# Build:
+#   docker build -t cascadingdev .
+#
+# Show help:
+#   docker run -it --rm cascadingdev
+#
+# Build installer bundle:
+#   docker run -it --rm -v $(pwd)/output:/output cascadingdev \
+#     bash -c "cdev build && cp -r install/* /output/"
+#
+# Install into a new project (headless):
+#   docker run -it --rm -v /path/to/project:/project cascadingdev \
+#     python install/cascadingdev-*/setup_cascadingdev.py --target /project --no-ramble
+#
+# Interactive shell:
+#   docker run -it --rm cascadingdev bash

docker-compose.yml

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+# CascadingDev Simplified - Docker Compose
+#
+# Quick Start:
+#   docker-compose build          # Build the image
+#   docker-compose run --rm cli   # Show help
+#   docker-compose run --rm build # Build installer bundle
+#   docker-compose run --rm shell # Interactive shell
+
+version: '3.8'
+
+services:
+  # ============================================================================
+  # CLI (show help)
+  # ============================================================================
+  cli:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    image: cascadingdev:latest
+    command: ["cdev", "--help"]
+
+  # ============================================================================
+  # Build installer bundle
+  # ============================================================================
+  build:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    image: cascadingdev:latest
+    volumes:
+      - ./output:/output
+    command: ["bash", "-c", "cdev build && cp -r install/* /output/ && echo 'Installer bundle copied to ./output/'"]
+
+  # ============================================================================
+  # Test installation (creates project in /tmp)
+  # ============================================================================
+  test-install:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    image: cascadingdev:latest
+    command: >
+      bash -c "
+        cdev build &&
+        python install/cascadingdev-*/setup_cascadingdev.py --target /tmp/test-project --no-ramble &&
+        echo '=== Installation successful ===' &&
+        ls -la /tmp/test-project/ &&
+        echo '=== Pre-commit hook ===' &&
+        cat /tmp/test-project/.git/hooks/pre-commit | head -30
+      "
+
+  # ============================================================================
+  # GUI (requires X11 forwarding)
+  # ============================================================================
+  gui:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    image: cascadingdev:latest
+    environment:
+      - DISPLAY=${DISPLAY:-:0}
+      - QT_QPA_PLATFORM=xcb
+    volumes:
+      - /tmp/.X11-unix:/tmp/.X11-unix:ro
+      - ./output:/output
+    command: >
+      bash -c "
+        cdev build &&
+        python install/cascadingdev-*/setup_cascadingdev.py --target /output/test-project
+      "
+    network_mode: host
+
+  # ============================================================================
+  # Interactive Shell
+  # ============================================================================
+  shell:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    image: cascadingdev:latest
+    volumes:
+      - ./output:/output
+    command: ["/bin/bash"]
+    stdin_open: true
+    tty: true
+
+# ==============================================================================
+# Usage Examples
+# ==============================================================================
+#
+# Build image:
+#   docker-compose build
+#
+# Show CLI help:
+#   docker-compose run --rm cli
+#
+# Build installer bundle (outputs to ./output/):
+#   docker-compose run --rm build
+#
+# Test installation in container:
+#   docker-compose run --rm test-install
+#
+# Interactive shell:
+#   docker-compose run --rm shell
+#
+# GUI with Ramble (requires: xhost +local:docker):
+#   docker-compose run --rm gui