Performance improvements: fix MCP server shutdown and disable caching

- Add proper shutdown handling for MCP servers
  - Listen for stdin EOF (main issue causing 6min delays)
  - Add transport.close() to properly close connections
  - Add 5-minute timeout safety net
  - Handle SIGHUP signal
- Disable Bun caching to avoid timeout errors
- Add Dockerfile.runner for pre-built container option
- Create optimized workflow example without container layer

Dockerfile.runner

@@ -0,0 +1,26 @@
+FROM node:18-slim
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y \
+    git \
+    curl \
+    unzip \
+    ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+# Install Bun globally
+RUN curl -fsSL https://bun.sh/install | bash && \
+    ln -s /root/.bun/bin/bun /usr/local/bin/bun
+
+# Pre-install Claude Code and dependencies
+WORKDIR /opt/claude-action
+COPY package.json bun.lockb* ./
+RUN bun install --frozen-lockfile
+
+# Install claude-code globally
+RUN bun add -g @anthropic-ai/claude-code@1.0.62
+
+# Set up environment
+ENV PATH="/root/.bun/bin:${PATH}"
+
+WORKDIR /workspace