fix(infra): unblock docker builds for stars agent and web

- Dockerfile.ml: install build-essential so pyswisseph (stars agent) compiles
- Dockerfile.web: copy root package.json + pnpm-workspace.yaml + pnpm-lock.yaml into builder stage so pnpm --filter resolves the workspace
- CLAUDE.md: record both gotchas alongside the existing Docker rebuild notes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

infra/docker/Dockerfile.ml

@@ -1,5 +1,8 @@
 FROM python:3.12-slim
 WORKDIR /app/ml/serving
+RUN apt-get update \
+ && apt-get install -y --no-install-recommends build-essential \
+ && rm -rf /var/lib/apt/lists/*
 COPY ml/serving/requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 COPY ml/ /app/ml/