feat: add tool-images directory with Dockerfiles for all base tool types

- Create tool-images/ directory with organized Dockerfile templates
- Add base.dockerfile with common dev tools (git, nvim, ranger, tmux, node)
- Add code-server.dockerfile with VS Code in browser
- Add jupyter.dockerfile with Jupyter Lab
- Add opencode.dockerfile with OpenCode agent
- Add pi-agent.dockerfile with Pi Coding Agent (pi.dev)
- All images include: git, neovim, ranger, tmux, htop, tree, jq, Node.js 20
- Add README with usage instructions

tool-images/opencode.dockerfile

@@ -0,0 +1,40 @@
+# OpenCode agent environment
+FROM ubuntu:24.04
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+# Install base dependencies
+RUN apt-get update && apt-get install -y \
+    curl \
+    wget \
+    git \
+    neovim \
+    ranger \
+    tmux \
+    htop \
+    tree \
+    jq \
+    ca-certificates \
+    python3 \
+    python3-pip \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install Node.js
+RUN curl -fsSL https://deb.nodesource.com/setup_20.x | bash - \
+    && apt-get install -y nodejs \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install OpenCode
+RUN npm install -g opencode
+
+# Create non-root user
+RUN useradd -m -s /bin/bash user
+WORKDIR /home/user
+
+# Set up git
+RUN git config --global init.defaultBranch main
+
+USER user
+
+EXPOSE 3000
+CMD ["opencode", "server"]