chore(test,docs): add make test, CI, e2e container, refresh example

- Makefile gains `test` and `test-e2e` targets; `deps` now installs the
  dev extras so pytest is available after `make deps`.
- .github/workflows/test.yml runs unit tests on push and PR to main
  (Python 3.13 on ubuntu-latest, ignores tests/e2e by default).
- tests/e2e/Containerfile + test_dotfiles_e2e.py scaffold a real
  container-based smoke test of `flow dotfiles init` + `link` against
  the example dotfiles repo. Gated by FLOW_RUN_E2E=1 so unit runs
  stay fast; verified locally with podman.
- tests/fakes.FakeRunner uses ordered subsequence matching instead of
  unordered containment -- prevents accidental match between unrelated
  commands that happen to share tokens.
- example/README.md rewritten for the current command surface
  (no more `dotfiles undo`, `dotfiles modules ...`, `--relink`,
  `bootstrap list/show/run --profile`, `bootstrap packages --resolved`).
  Adds an "External modules" section documenting `_module.yaml`.
- example/dotfiles-repo profiles.yaml drops `allow-sudo: true` along
  with the runtime support.
- pyproject.toml adds [tool.coverage] config.

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

tests/e2e/Containerfile

@@ -0,0 +1,37 @@
+# Containerfile for end-to-end testing of the flow CLI.
+#
+# Builds a minimal Debian image with python + git, copies the flow source in,
+# installs it via pip, and creates a non-root user (flow refuses to run as root).
+#
+# Build context expected to be the flow-cli repo root. Example:
+#   podman build -f tests/e2e/Containerfile -t flow-e2e .
+#
+FROM debian:bookworm-slim
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+        git \
+        python3 \
+        python3-venv \
+        python3-pip \
+        sudo \
+        ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+
+# Create a non-root user; flow refuses to run as uid 0.
+RUN useradd --create-home --shell /bin/bash flowuser \
+    && echo "flowuser ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers
+
+# Copy the flow source and install it for the non-root user.
+WORKDIR /opt/flow-src
+COPY --chown=flowuser:flowuser . /opt/flow-src
+
+USER flowuser
+ENV PATH="/home/flowuser/.local/bin:${PATH}"
+
+RUN pip3 install --user --break-system-packages -e /opt/flow-src
+
+WORKDIR /home/flowuser
+ENTRYPOINT ["/bin/bash"]

tests/e2e/__init__.py

@@ -0,0 +1 @@
+"""End-to-end tests gated by FLOW_RUN_E2E=1."""

tests/e2e/test_dotfiles_e2e.py

@@ -0,0 +1,88 @@
+"""End-to-end test for `flow dotfiles` against the example repo.
+
+Gated by FLOW_RUN_E2E=1 because it builds and runs a container image.
+Tries podman first, falls back to docker. Skips if neither is available.
+"""
+
+from __future__ import annotations
+
+import os
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+CONTAINERFILE = Path(__file__).parent / "Containerfile"
+EXAMPLE_REPO = REPO_ROOT / "example" / "dotfiles-repo"
+IMAGE_TAG = "flow-e2e:test"
+
+
+def _pick_runtime() -> str | None:
+    for binary in ("podman", "docker"):
+        if shutil.which(binary):
+            return binary
+    return None
+
+
+@pytest.mark.skipif(
+    os.environ.get("FLOW_RUN_E2E") != "1",
+    reason="set FLOW_RUN_E2E=1 to run",
+)
+def test_dotfiles_init_and_link_in_container():
+    runtime = _pick_runtime()
+    if runtime is None:
+        pytest.skip("neither podman nor docker is available")
+
+    build = subprocess.run(
+        [
+            runtime, "build",
+            "-f", str(CONTAINERFILE),
+            "-t", IMAGE_TAG,
+            str(REPO_ROOT),
+        ],
+        capture_output=True,
+        text=True,
+    )
+    if build.returncode != 0:
+        pytest.fail(f"image build failed:\n{build.stdout}\n{build.stderr}")
+
+    try:
+        # Run flow inside the container against the mounted example repo.
+        # `flow dotfiles init` clones, so we need a real git remote — turn
+        # the read-only example mount into a bare-ish working repo first.
+        script = (
+            "set -eux; "
+            "cp -r /example /home/flowuser/dotfiles-src; "
+            "cd /home/flowuser/dotfiles-src; "
+            "git init -q -b main; "
+            "git -c user.email=e2e@example.com -c user.name=e2e add -A; "
+            "git -c user.email=e2e@example.com -c user.name=e2e commit -q -m initial; "
+            "cd /home/flowuser; "
+            "flow dotfiles init --repo /home/flowuser/dotfiles-src; "
+            "flow dotfiles link --profile linux-auto --dry-run; "
+            "flow dotfiles status"
+        )
+        result = subprocess.run(
+            [
+                runtime, "run", "--rm",
+                "-v", f"{EXAMPLE_REPO}:/example:ro",
+                IMAGE_TAG,
+                "-c", script,
+            ],
+            capture_output=True,
+            text=True,
+        )
+        assert result.returncode == 0, (
+            f"e2e run failed (rc={result.returncode}):\n"
+            f"stdout: {result.stdout}\n"
+            f"stderr: {result.stderr}"
+        )
+    finally:
+        subprocess.run(
+            [runtime, "rmi", "-f", IMAGE_TAG],
+            capture_output=True,
+            text=True,
+        )