feat: Add handler-base library for NATS AI/ML services

- Handler base class with graceful shutdown and signal handling
- NATSClient with JetStream and msgpack serialization
- Pydantic Settings for environment configuration
- HealthServer for Kubernetes probes
- OpenTelemetry telemetry setup
- Service clients: STT, TTS, LLM, Embeddings, Reranker, Milvus

Dockerfile

@@ -0,0 +1,58 @@
+# Handler Base Image
+#
+# Provides a pre-built base with all common dependencies for handler services.
+# Services extend this image and add their specific code.
+#
+# Build:
+#   docker build -t ghcr.io/billy-davies-2/handler-base:latest .
+#
+# Usage in child Dockerfile:
+#   FROM ghcr.io/billy-davies-2/handler-base:latest
+#   COPY my_handler.py .
+#   CMD ["python", "my_handler.py"]
+
+FROM python:3.13-slim AS base
+
+WORKDIR /app
+
+# Install uv for fast, reliable package management
+COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    curl \
+    && rm -rf /var/lib/apt/lists/*
+
+# Copy and install handler-base package
+COPY pyproject.toml README.md ./
+COPY handler_base/ ./handler_base/
+
+# Install the package with all dependencies
+RUN uv pip install --system --no-cache .
+
+# Set environment variables
+ENV PYTHONUNBUFFERED=1
+ENV PYTHONDONTWRITEBYTECODE=1
+
+# Default health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=10s --retries=3 \
+    CMD curl -f http://localhost:8080/health || exit 1
+
+# Default command (override in child images)
+CMD ["python", "-c", "print('handler-base ready')"]
+
+
+# Audio variant with soundfile, librosa, webrtcvad
+FROM base AS audio
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ffmpeg \
+    libsndfile1 \
+    gcc \
+    python3-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN uv pip install --system --no-cache \
+    soundfile>=0.12.0 \
+    librosa>=0.10.0 \
+    webrtcvad>=2.0.10