ci: lean Dockerfile (drop build-essential), split+timeout build steps, buildkit

Dockerfile

@@ -1,25 +1,16 @@
 FROM python:3.12-slim
 
-# Set working directory
 WORKDIR /app
 
-# Install build dependencies and Python build backend
-RUN apt-get update \
-    && apt-get install -y --no-install-recommends \
-       build-essential \
-       curl \
-    && rm -rf /var/lib/apt/lists/*
-
-# Install Python build tool
-RUN pip install --no-cache-dir hatchling
-
 # Copy project files
 COPY pyproject.toml pyproject.toml
 COPY src src
 COPY README.md README.md
 COPY .env.example .env.example
 
-# Install the package and runtime dependencies
+# Install the package and runtime dependencies. All dependencies ship as
+# manylinux wheels (pydantic-core, cryptography, etc.), so no build toolchain
+# is required — keeping the image small and the build fast.
 RUN pip install --no-cache-dir .
 
 # Run the MCP server. Transport is selected via MCP_TRANSPORT (default stdio);