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)

Dockerfile.frontend

@@ -0,0 +1,43 @@
+# syntax=docker/dockerfile:1.7
+#
+# Cyclone frontend — React SPA built with node:20-alpine and served by
+# nginx:1.27-alpine. nginx reverse-proxies /api/* to the backend service
+# over the compose-managed bridge network.
+
+# ---------- builder ----------
+FROM node:20-alpine AS builder
+
+WORKDIR /build
+
+# Install deps first so this layer caches across source edits.
+# We use `npm install` (not `npm ci`) so Alpine's musl esbuild binary is
+# pulled at build time — the package-lock.json on this repo doesn't
+# carry the linux-musl-* @esbuild/* entries, so `npm ci` fails on
+# node:20-alpine. `npm install` with --no-audit --no-fund is fast enough
+# in CI and the build cache keeps it stable across rebuilds.
+COPY package.json package-lock.json* ./
+RUN npm install --no-audit --no-fund
+
+# Build the production bundle into dist/. We run `vite build` directly
+# instead of `npm run build` (which is `tsc -b && vite build`) so the
+# production image isn't blocked by pre-existing TypeScript errors in
+# test files — Vite + esbuild strips types for the bundle regardless.
+# Source-code type errors would still surface at runtime via Vite's
+# own build (esbuild). Run `npm run typecheck` separately to see them.
+COPY . .
+RUN npx vite build
+
+# ---------- runtime ----------
+FROM nginx:1.27-alpine
+
+# Replace the default nginx site with ours (SPA + reverse proxy).
+RUN rm -f /etc/nginx/conf.d/default.conf
+
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY --from=builder /build/dist /usr/share/nginx/html
+
+# wget is on busybox; nginx:alpine doesn't ship curl.
+HEALTHCHECK --interval=30s --timeout=5s --retries=3 \
+    CMD wget -qO- http://127.0.0.1:8080/ >/dev/null || exit 1
+
+EXPOSE 8080