feat(llm-gateway): implement LLM Gateway MCP Server (#56)

Implements complete LLM Gateway MCP Server with:
- FastMCP server with 4 tools: chat_completion, list_models, get_usage, count_tokens
- LiteLLM Router with multi-provider failover chains
- Circuit breaker pattern for fault tolerance
- Redis-based cost tracking per project/agent
- Comprehensive test suite (209 tests, 92% coverage)

Model groups defined per ADR-004:
- reasoning: claude-opus-4 → gpt-4.1 → gemini-2.5-pro
- code: claude-sonnet-4 → gpt-4.1 → deepseek-coder
- fast: claude-haiku → gpt-4.1-mini → gemini-2.0-flash

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

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

mcp-servers/llm-gateway/Dockerfile

@@ -0,0 +1,53 @@
+# Syndarix LLM Gateway MCP Server
+# Multi-stage build for minimal image size
+
+# Build stage
+FROM python:3.12-slim AS builder
+
+# Install uv for fast package management
+COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
+
+WORKDIR /app
+
+# Copy dependency files
+COPY pyproject.toml ./
+
+# Create virtual environment and install dependencies
+RUN uv venv /app/.venv
+ENV PATH="/app/.venv/bin:$PATH"
+RUN uv pip install -e .
+
+# Runtime stage
+FROM python:3.12-slim AS runtime
+
+# Create non-root user for security
+RUN groupadd --gid 1000 appgroup && \
+    useradd --uid 1000 --gid appgroup --shell /bin/bash --create-home appuser
+
+WORKDIR /app
+
+# Copy virtual environment from builder
+COPY --from=builder /app/.venv /app/.venv
+ENV PATH="/app/.venv/bin:$PATH"
+
+# Copy application code
+COPY --chown=appuser:appgroup . .
+
+# Switch to non-root user
+USER appuser
+
+# Environment variables
+ENV LLM_GATEWAY_HOST=0.0.0.0
+ENV LLM_GATEWAY_PORT=8001
+ENV PYTHONUNBUFFERED=1
+ENV PYTHONDONTWRITEBYTECODE=1
+
+# Expose port
+EXPOSE 8001
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
+    CMD python -c "import httpx; httpx.get('http://localhost:8001/health').raise_for_status()" || exit 1
+
+# Run the server
+CMD ["python", "server.py"]