REPO_POLICIES: move the example Dockerfiles into examples/

Each fenced dockerfile block moves byte for byte into its own file
under examples/, and one sentence links it where the block stood.
Phrases that pointed at a block by position now name the file. Both
checklists name the files. Rules keep their wording.

As #159 (comment) says.

Model: opus-5-5

examples/python-test-phase.Dockerfile

@@ -0,0 +1,24 @@
+# Test phase. Both pytest runs share one 90-second timeout, so a hang
+# uses it once and gets no rerun.
+# debian:trixie-slim, YYYY-MM-DD
+FROM debian@sha256:... AS test
+# Python, pip and venv come from the distribution, which is trusted, so
+# they need no version and no hash. make and git are base tools that
+# script/bootstrap installs when they are missing. Installed here, they
+# stay in their own layer when script/ changes.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates make git \
+        python3 python3-venv \
+    && rm -rf /var/lib/apt/lists/*
+# script/bootstrap installs pipenv in a virtual environment at
+# $HOME/.pipenv, and the tests below run that pipenv.
+ENV PATH=/root/.pipenv/bin:$PATH
+WORKDIR /app
+COPY script/ script/
+COPY Pipfile Pipfile.lock ./
+RUN script/bootstrap
+ARG CACHEBUST
+COPY . .
+RUN timeout 90 sh -c 'pipenv run pytest || { \
+        echo "--- Rerunning with -v for details ---"; \
+        pipenv run pytest -v; exit 1; }'