Split docker-compose into production (pull) and dev (build) files

docker-compose.yml now pulls the pre-built image from
gitea.labsconnect.se/bobban/scheduletaskmanager-schedule-task-manager:latest
instead of building locally; the old build-from-source file moves to
docker-compose.dev.yml for local testing or before a push pipeline
exists. README documents both paths.

README.md

@@ -38,12 +38,30 @@ In Authentik:
 ```sh
 cp .env.example .env
 # edit .env: APP_BASE_URL, SESSION_SECRET, AUTHENTIK_*
-
-docker compose up -d --build
 ```
 
-The app listens on `HOST_PORT` (default `3000`). SQLite data and session
-files persist in `./data` on the host.
+Two compose files, depending on where the image comes from:
+
+- **`docker-compose.yml`** (production) — pulls
+  `gitea.labsconnect.se/bobban/scheduletaskmanager-schedule-task-manager:latest`.
+  Requires that image to already exist at that tag (pushed manually or by a
+  CI pipeline) and, if the registry is private, `docker login gitea.labsconnect.se`
+  first.
+
+  ```sh
+  docker compose pull
+  docker compose up -d
+  ```
+
+- **`docker-compose.dev.yml`** — builds the image locally from source instead
+  of pulling. Use this for local testing or before a build pipeline exists.
+
+  ```sh
+  docker compose -f docker-compose.dev.yml up -d --build
+  ```
+
+Either way, the app listens on `HOST_PORT` (default `3000`), and SQLite data
+and session files persist in `./data` on the host.
 
 ## 3. Local development