fix(docker): build the image from uv.lock too

The other half of #2194. The runtime stage did `COPY pyproject.toml .` +
`pip install .` and never copied uv.lock at all, so the SHIPPED IMAGE
resolved its own dependency set — independently of CI and of the lock. CI
could be green on one set of versions while the published image ran another,
which makes a green run evidence about the tests and not about the artifact.

Now: install uv, sync deps from the lock, then sync the project. Split into
two syncs so the dependency layer caches on any build that doesn't touch the
lock — the same shape CI uses, so image and CI can no longer disagree.

`uv sync` installs into /app/.venv rather than the system interpreter, so PATH
picks it up for the alembic + hypercorn CMD. The project stays editable, which
keeps /app/src authoritative exactly as PYTHONPATH and the frontend-dist copy
into src/scribe/static/ already assume.

Not built locally (rules #10/#12) — the dev build job verifies it, and `main`
already carries a working :latest, so a break here can't strand a deploy.

Dockerfile

@@ -12,10 +12,27 @@ RUN npm run build
 FROM python:3.14-slim AS runtime
 WORKDIR /app
 
-COPY pyproject.toml .
-COPY src/ src/
+# Installed from uv.lock, exactly like CI (issue #2194). This used to be
+# `COPY pyproject.toml .` + `pip install .`, which never even copied the lock:
+# the shipped image resolved its own dependency set, so CI could be green on one
+# set of versions while the published image ran another. On 2026-07-28 that
+# class of drift turned `main` red when mcp 2.0.0 shipped mid-session.
 RUN --mount=type=cache,target=/root/.cache/pip \
-    pip install .
+    pip install --no-cache-dir uv
+
+# Dependencies before source, so the expensive layer is cached on every build
+# that doesn't change the lock.
+COPY pyproject.toml uv.lock ./
+RUN --mount=type=cache,target=/root/.cache/uv \
+    uv sync --locked --no-dev --no-install-project
+
+COPY src/ src/
+RUN --mount=type=cache,target=/root/.cache/uv \
+    uv sync --locked --no-dev
+
+# uv sync installs into a project venv rather than the system interpreter, so
+# alembic and hypercorn in CMD have to be found there.
+ENV PATH="/app/.venv/bin:$PATH"
 
 COPY --from=build-frontend /build/dist/ src/scribe/static/
 COPY alembic.ini .