fix: restore COPY/RUN lines in Dockerfile

Previous commit's regex substitution dropped `COPY requirements.txt .`
and the initial `RUN pip install --no-cache-dir -r requirements.txt`
because of a bash-heredoc escape interaction (the \1 backref was
consumed before the python regex saw it, leaving a SOH char). This
restores both lines with the conditional version-pin upgrade after.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -16,7 +16,9 @@ WORKDIR /app
 # ARG changes the cache key for the pip install layer below — the
 # fix for the cascade cache trap that bit us 5x on 2026-04-27.
 ARG RUNTIME_VERSION=
-
 && \
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt && \
     if [ -n "${RUNTIME_VERSION}" ]; then \
       pip install --no-cache-dir --upgrade "molecule-ai-workspace-runtime==${RUNTIME_VERSION}"; \
     fi