Ship the API docs the container never had, and theme them like the product

/api/docs was broken in every Docker deployment, including the air-gapped ones.
docs.py resolves openapi.json and llms.txt from the repo root, and the image
copies shopdb, plugins, migrations, scripts and wsgi.py but never docs. The page
rendered the Redoc shell and then answered 404 fetching its own specification.
Only the two files the app actually serves are copied; the rest of that tree is
prose with no business in a runtime image.

The theme was invented colours that matched nothing. It now maps the product's
own tokens, and reads the theme the way the app does: the application stores an
explicit light/dark choice and stamps data-theme, so choosing light on a
dark-desktop kiosk used to give a dark documentation page. The operating system
setting is the fallback, exactly as it is in the app.

Light-mode primary, success and error are a shade darker than the product
tokens, because those tokens are designed as fills and fail contrast as text on
the nested panels where type names and required labels sit. Measured with a
browser harness rather than judged by eye: every text node in both themes now
clears WCAG AA, from an initial 5603 reported failures - most of which were the
harness itself ignoring alpha, which is its own lesson about trusting a number.

Four Redoc elements carry hardcoded colours with no theme key and keep targeted
rules, selected by tag and attribute rather than by generated class hashes that
change on every build.

The build now compiles the Python. Docker never imports the application, so a
syntax error sails through every layer and surfaces as a crash-looping
container; that happened, four restarts, while working on this file.

Redoc's upstream licence file was never vendored although its bundle header
points at it. The placeholder added here says exactly that rather than inventing
the third-party notices it is supposed to carry, and the dead redocly.com badge
is hidden: the licence wants the notice in the distribution, not a rendered
link that a site with no internet cannot follow.

(cherry picked from commit 6c00b10618)

Dockerfile

@@ -133,6 +133,20 @@ COPY wsgi.py ./
 # Make entrypoint and bootstrap scripts executable
 RUN chmod +x /app/scripts/docker-entrypoint.sh /app/scripts/bootstrap-plugins.sh
 
+# The two files under docs/ that the APP SERVES at runtime, not documentation.
+# shopdb/core/api/docs.py resolves both relative to the repo root, so without
+# them /api/docs renders the Redoc shell and then 404s fetching its own spec -
+# which is what every Docker deployment did. Copied by name rather than copying
+# docs/ wholesale: the rest of that tree is prose and has no business in a lean
+# runtime image.
+COPY docs/openapi.json docs/llms.txt ./docs/
+
+# Fail the BUILD on a syntax error rather than the pod at runtime. Docker never
+# imports the application, so a broken .py sails through every layer and only
+# surfaces as a crash-looping container: observed, four restarts before anyone
+# noticed. compileall touches nothing at runtime and costs a couple of seconds.
+RUN python -m compileall -q shopdb plugins migrations wsgi.py
+
 # Built SPA from stage 1. Flask serves it via register_frontend_routes.
 COPY --from=frontendbuild /build/frontend/dist ./frontend/dist