refactor: give the frontend its own directory and split the API into routers

The Site's page sat at the repository root while its scripts lived in
local/static, a split with no reason behind it. They are together in web/ now,
with the page as index.html, which is also what the image serves.

app.py held the adapters, the configuration, the shared query helpers and
nineteen routes; customer.py held fourteen more but could not import from it
without a cycle, so it was wired by passing nine callables into install_routes.
Configuration and shared helpers move to local/runtime.py, the rules for
attaching artwork to an order move to local/artwork.py where a customer
correction and an operator final-file set can share them, and the routes become
seven routers under local/api. app.py is 48 lines that create the application,
apply the middleware and include them. Routers import downwards only.

Three faults came out of the extraction and are worth recording, because each
passed a check that looked sufficient. ast reports a function's line at the def,
so every decorator on the line above fell outside the extracted range: twelve
routes and the security middleware were defined but never registered, and the
files still imported and parsed cleanly. Names the old closure renamed on the
way in, and a Jsonb import, were missing in three modules. A name-resolution
pass over every new module found those; the route count matching the original
exactly, 32, is what confirmed the first.

The release gate's marker for the fake payment adapter pointed at app.py and the
adapter moved to runtime.py, so the gate passed while the condition it guards was
unchanged. That is the same silent decay 2.5 set out to fix. A test now asserts
every marker still matches something in its file, so the next move fails loudly.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/vendor/README.md

@@ -0,0 +1,33 @@
+# Vendored third-party assets
+
+Served from this repository rather than a CDN, so the Site does not depend on a
+third party being reachable and honest at the moment a customer opens it, and so
+the Content-Security-Policy can name only `'self'` for scripts and workers.
+
+## pdf.js 3.11.174
+
+Used by the by-metre flow to measure and rasterise a PDF sheet in the browser.
+
+| File | SHA-256 |
+|---|---|
+| `pdf.min.js` | `5b5799e6f8c680663207ac5b42ee14eed2a406fa7af48f50c154f0c0b1566946` |
+| `pdf.worker.min.js` | `feabdf309770ed24bba31a5467836cdc8cf639c705af27d52b585b041bb8527b` |
+
+Downloaded from `https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/` and
+verified against the SRI digests cdnjs publishes for that release:
+
+```
+pdf.min.js         sha512-q+4liFwdPC/bNdhUpZx6aXDx/h77yEQtn4I1slHydcbZK34nLaR3cAeYSJshoxIOq3mjEf7xJE8YWIUHMn+oCQ==
+pdf.worker.min.js  sha512-BbrZ76UNZq5BhH7LL7pn9A4TKQpQeNCHOo65/akfelcIBbcVvYWOFQKPXIrykE3qZxYjmDX573oa4Ywsc7rpTw==
+```
+
+To verify or refresh, compare against that API before replacing anything:
+
+```bash
+curl -s "https://api.cdnjs.com/libraries/pdf.js/<version>?fields=sri"
+```
+
+**Version note.** 3.11.174 is old. It is affected by GHSA-wgrm-67xf-hhpq, whose
+documented workaround is `isEvalSupported: false`; `web/index.html` already passes
+that, so the known path is closed. Upgrading is worthwhile but is an API change,
+not a file swap, and belongs with its own browser testing — see `ROADMAP.md` 2.7.