fix(docker): add g++ for isotree build, add dashboard Dockerfile.tests

- bot-detector Dockerfile + Dockerfile.tests: install g++ for isotree C++ extension
- dashboard Dockerfile.tests: new smoke test (verify FastAPI app loads)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

services/bot-detector/bot_detector/Dockerfile.tests

@@ -1,5 +1,7 @@
 FROM python:3.11-slim
 WORKDIR /app
+# Build deps for isotree (C++ extension)
+RUN apt-get update && apt-get install -y --no-install-recommends g++ && rm -rf /var/lib/apt/lists/*
 COPY shared/python/ja4_common/ /app/shared/ja4_common/
 RUN pip install --no-cache-dir /app/shared/ja4_common/
 COPY services/bot-detector/bot_detector/requirements.txt .