docs(readme): describe the local setup

README.md

@@ -130,6 +130,26 @@ Tests sit next to the code they test (`Component.test.jsx`).
 
 ## Run locally
 
+### Local development without keys (profile `local`)
+
+The whole stack runs on your machine with no API keys and no calls to Steam, Twitch/IGDB or speedrun.com. Needs
+Java 25, Node 24 and Docker. Clone `ToBePlayed-Auth`, `ToBePlayed-Core` and `ToBePlayed-Frontend` next to each
+other, then start them in this order (Core also starts without Auth and finds it later):
+
+1. **Auth**: in `ToBePlayed-Auth`, `./mvnw spring-boot:run -Dspring-boot.run.profiles=local`
+   (IDE: active profile `local`). Port 8080.
+2. **Core**: in `ToBePlayed-Core`, `./mvnw spring-boot:run -Dspring-boot.run.profiles=local`. Port 8090.
+3. **Frontend**: in `ToBePlayed-Frontend`, `npm install`, then `npm run dev`, and open `http://localhost:5173`
+   (`localhost`, not `127.0.0.1`, so the browser sends the login cookies to every local port). The development
+   values must be `VITE_API_URL=http://localhost:8080` and `VITE_CORE_API_URL=http://localhost:8090`.
+4. **Log in** with `dev@localhost` / `password123`. On the dashboard, start a Steam sync: the library fills with 8
+   games, achievements, time to beat, moods, a wishlist and one speedrun game from recorded answers.
+
+The dev user is `PLATFORM_ADMIN`, so user, auditor and admin pages can all be tried ("View as" in the menu
+switches down). What the profile does in Auth and Core: their readmes, "Run locally".
+
+### Against other services
+
 Needs Node 24 and running Auth and Core services.
 
 ```bash