feat: 31 new tests, metrics LLM counters, Dockerfile caching, Makefile targets, compose limits, code fixes

Dockerfile

@@ -7,11 +7,16 @@ COPY --from=ghcr.io/astral-sh/uv:latest /uv /uvx /usr/local/bin/
 
 WORKDIR /app
 
-COPY pyproject.toml README.md ./
-COPY guarddog_nexus/ guarddog_nexus/
-
+# Install dependencies first for layer caching (source changes don't invalidate)
+COPY pyproject.toml ./
+RUN mkdir -p guarddog_nexus && echo '__version__ = "0.1.0"' > guarddog_nexus/__init__.py
 RUN uv pip install . --system
 RUN uv pip install --system "guarddog>=2.10.0"
+RUN rm -rf guarddog_nexus
+
+# Application source (frequently changes — cached dependency layers preserved)
+COPY guarddog_nexus/ guarddog_nexus/
+COPY README.md ./
 
 RUN mkdir -p /data /tmp/guarddog-nexus