feat(openzaak): one-command UI-OpenZaak bridge, real BSN fix, flake mitigation

scripts/openzaak-ui-up.sh brings up the root app and the OpenZaak harness
together, wires them onto one docker network, seeds the catalogus, grants
the container-alias zaaktype scope, and verifies a real aanvraag submitted
through the UI lands in OpenZaak.

Along the way: DocumentStore.DemoOwner was reusing the seeded doctor's
11-digit BIG-nummer as a stand-in BSN, which isn't a valid 9-digit BSN shape
— OpenZaak rejects it, breaking both submit's rol-creation step and the
citizen's own applications list under Zgw:Enabled=true. Fixed to a real
elfproef-valid BSN.

Also adds mitigation for a still-unexplained per-container flake (every
outbound ZGW POST fails as if the body were empty, for that container's
whole lifetime) that correlates with host memory pressure: the script now
warns when host swap is heavily used, and an opt-in ZgwDiagnosticHandler
(ZGW_DEBUG_HTTP=1) logs Content-Length vs. actual bytes sent so the next
reproduction can confirm or rule out client-side body corruption.

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

backend/openzaak/README.md

@@ -80,6 +80,42 @@ BFF_AUTH='<the same secret>' ./verify-notificatie.sh   # proves a real delivery,
 To go back to the fast, no-notifications default: `docker compose -f docker-compose.openzaak.yml
 up -d --remove-orphans` (drops the celery worker, restores `NOTIFICATIONS_DISABLED: 'true'`).
 
+## Testing the Angular UI against this harness
+
+The base harness above and the app's own root `docker-compose.yml` are independent projects on
+purpose (see the top of this file) — this is the opt-in bridge between them, for when you want
+to click through the real UI and see an aanvraag land in a real OpenZaak instead of just
+running `dotnet test`. One command from the repo root:
+
+```bash
+scripts/openzaak-ui-up.sh
+```
+
+It brings up the root app (so its docker network exists), brings up this harness plus
+`docker-compose.openzaak.bff.yml` (gives this harness's `web` service a dotted alias,
+`openzaak.local`, on its own network — the root project's `api` container joins THIS network,
+in the opposite direction from the notifications overlay below, to avoid a real alias
+collision: the root project's frontend service is also called `web`. The alias needs a dot
+because Django's URLValidator rejects a bare hostname in a URL field; this environment's
+rootless Podman also can't route container→host-port traffic through `host.docker.internal`,
+so container-to-container is the only reliable path either way — see that file's header
+comment for the full, empirically-confirmed reasoning), seeds the catalogus, additively
+replaces the zrc authorization grant to match the alias (ZGW authorization is scoped by the
+*exact* zaaktype URL string, not just the resource; see `scripts/openzaak-ui-up.sh`'s own
+comment for why this is a replace, not an add), and brings the root app back up pointed at
+OpenZaak (`docker-compose.openzaak.yml` at the repo root). A final self-check submits a
+throwaway aanvraag and confirms it actually lands in OpenZaak, restarting `api` (up to 5
+times) if not — see that script for a caveat about an intermittent per-container networking
+flake this environment can hit under memory pressure (the script now warns if host swap is
+already high going in; `ZGW_DEBUG_HTTP=1` on `api`, see `docker-compose.openzaak.yml`, logs
+diagnostics to help nail the cause next time it reproduces). Prints the URLs to check
+afterward and the teardown commands.
+
+Two caveats, both non-fatal (WP-60 catches and flags rather than surfacing an error):
+**only `herregistratie` has a seeded zaaktype** here, so submit that wizard to prove a real
+write; and **no Documenten content is seeded**, so a document upload's ZGW half no-ops (pick
+"per post" in the wizard's document step, or ignore it).
+
 ## Tear down
 
 ```bash