docs: point README at split backend repo

README.md

@@ -5,33 +5,24 @@ events (KCs), replacing the WordPress plugin "Workshop-Wahlen". See
 [plan-kcAppMultiTenantPlatform.prompt.md](plan-kcAppMultiTenantPlatform.prompt.md)
 for the full architecture and phased roadmap.
 
+This repo holds the **Flutter clients**. The backend (NestJS API) moved to
+its own repo: <https://git.konfi-castle.com/linus/KC-APP-Server>.
+
 ## Run with Docker
 
+See the [KC-APP-Server README](https://git.konfi-castle.com/linus/KC-APP-Server)
+for the backend/Docker setup. It expects a pre-built web bundle:
+
 ```bash
-cp backend/.env.example backend/.env               # fill in the secrets
-# optional (push): put the Firebase service account at backend/serviceAccount.json
-(cd client/app && flutter build web --release)     # host build — see note below
-docker compose up --build
+(cd client/app && flutter build web --release)
 ```
 
-`docker-compose.yml` starts PostgreSQL 16 and one `api` container (2-stage
-`Dockerfile`: NestJS build → slim runtime). The container runs
-`prisma migrate deploy` on start and serves the whole app — Flutter web
-client + REST API — on <http://localhost:3000>. Requires Docker Compose v2.
-
-The Flutter web bundle is built **on the host** and copied in (a Flutter
-builder stage would pull a ~2.8 GB SDK image). So `flutter build web` must
-run before `docker compose build`. Secrets come from `backend/.env`
-(unquoted, Compose v2 strips quotes) and the service-account JSON is
-bind-mounted read-only — neither is baked into the image.
+By default the server's `docker-compose.yml` mounts `../KC-APP/client/app/build/web`
+(sibling checkout); override with `WEB_CLIENT_BUILD_PATH` if your layout
+differs.
 
 ## Structure
 
-- `backend/` — NestJS API (Prisma/PostgreSQL, Authentik OIDC as resource
-  server, guest/Konfi local accounts, roles/permissions foundation, file
-  sharing, chat, local/cloud sync). See [backend/README.md](backend/README.md)
-  for setup. Also serves the web client (see below) directly, so it's the
-  single entry point for the web experience.
 - `client/app/` — the Flutter client (single codebase; **web** target
   enabled, mobile/desktop can be added later). Login (guest / local Teamer /
   invite redemption), role-aware home, guest Workshop-Wahl, file list,