feat(sp23): live-verification fixes from end-to-end bring-up

After the 8-commit SP23 implementation landed, kicking the tires on
`docker compose build && docker compose up -d` (the gated DOCKER_TESTS=1
live test) surfaced five real bugs that don't show up in unit tests:

1. Backend wheel was built from the stub `__init__.py`, not the real
   source. The Dockerfile's 'stub __init__, wheel, copy src, wheel
   again' pattern silently kept the first wheel's contents — only
   `__init__.py` got re-stubbed. The installed package had an empty
   `__init__.py`, so `from cyclone import __version__` failed at import
   time and the backend kept crashing in a restart loop.
   Fix: single `COPY src/` + single `pip wheel`. Comment explains
   why the stub trick is gone for good.

2. Backend binds to 127.0.0.1 (intentional — local-only by design,
   see CLAUDE.md). But that means the frontend container can't reach
   it over the compose bridge network — nginx got 'Connection refused'.
   Fix: `CYCLONE_HOST` env var, defaults to 127.0.0.1 (preserves local
   posture for non-Docker runs), set to 0.0.0.0 by the docker-compose
   backend service. Network isolation is provided by the compose bridge
   network (only `cyclone-frontend` joins).

3. Healthcheck probed `/api/healthz` (404 — the route is `/api/health`).
   Same in: backend Dockerfile HEALTHCHECK, docker-compose healthcheck,
   nginx.conf doesn't have one (frontend proxies through), RUNBOOK.md,
   scripts/post-deploy.sh, scripts/smoke.sh.
   Fix: `/api/healthz` → `/api/health` everywhere SP23 owns.

4. The auth matrix in `cyclone.auth.permissions` had
   `("GET", "/api/healthz"): set()` — which is the WRONG path (the
   route is `/api/health`). So even after fixing the healthcheck URL,
   the public auth bypass wouldn't have applied to `/api/health` and
   it would have been DENY-by-default (fail-closed).
   Fix: matrix entry updated to `/api/health`.

5. nginx upstream pointed at `cyclone-backend` (the project+service
   name), but compose v2 only resolves the bare service name (`backend`)
   over the bridge network. nginx crashed at config-load with 'host not
   found in upstream cyclone-backend'.
   Fix: `cyclone-backend:8000` → `backend:8000` in nginx.conf + spec
   + plan.

6. Frontend HEALTHCHECK used `http://localhost:8080/`. nginx in the
   alpine image listens on IPv6 (per the entrypoint's IPv6-by-default
   script), so `localhost` (which prefers IPv6 `::1` in musl) connects,
   but the resolved flow inside wget is unreliable. `127.0.0.1` works.
   Fix: HEALTHCHECK uses `http://127.0.0.1:8080/`.

Also moves `frontend/Dockerfile` → `Dockerfile.frontend` and
`frontend/nginx.conf` → `nginx.conf` at repo root (because the
frontend lives at the repo root, not in `frontend/`, and compose's
`build.context: .` needs them at the same root as compose.yml).
The frontend's pre-existing `.dockerignore` was empty/unused, so it's
dropped — the root `.dockerignore` covers it.

Adds `docker-compose.override.yml` for local bring-up testing on a
host without sudo. Production uses `/etc/cyclone/secrets/` directly.

Verified end-to-end on this dev host with `DOCKER_TESTS=1`:
- Both containers `(healthy)` within ~60s
- `curl http://localhost:8080/api/health` → 200 with valid JSON
- Login as admin → 200, /api/auth/me → 200
- `POST /api/parse-837` with docs/goodclaim.x12 → 200, batch created
- Full backend test suite: 1014 passed, 9 skipped (prodfiles gitignored)

docker-compose.yml

@@ -43,6 +43,11 @@ services:
       # embedding the secret in the compose file.
       CYCLONE_ADMIN_USERNAME_FILE: "/run/secrets/cyclone_admin_username"
       CYCLONE_ADMIN_PASSWORD_FILE: "/run/secrets/cyclone_admin_password"
+      # Bind 0.0.0.0 so the frontend container on the compose bridge
+      # network can reach us. The bridge network provides isolation —
+      # only the `frontend` service is on it; the host firewall still
+      # blocks anything that isn't on the LAN.
+      CYCLONE_HOST: "0.0.0.0"
     secrets:
       - cyclone_db_key
       - cyclone_admin_username
@@ -54,7 +59,7 @@ services:
       - cyclone_sftp_staging:/var/lib/cyclone/sftp_staging
       - cyclone_logs:/var/log/cyclone
     healthcheck:
-      test: ["CMD", "curl", "-fs", "http://localhost:8000/api/healthz"]
+      test: ["CMD", "curl", "-fs", "http://localhost:8000/api/health"]
       interval: 30s
       timeout: 5s
       retries: 3
@@ -65,7 +70,8 @@ services:
   frontend:
     image: cyclone-frontend:${TAG:-stable}
     build:
-      context: ./frontend
+      context: .
+      dockerfile: Dockerfile.frontend
     restart: unless-stopped
     ports:
       # LAN-bind: only this port is published to the host. The operator