docs(config): add media mode and TURN/recording env guidance

Backend/.env.example

@@ -11,5 +11,13 @@ MINIO_SECRET_KEY=minioadmin
 MINIO_BUCKET=videos
 MINIO_REGION=us-east-1
 MINIO_PRESIGNED_EXPIRY_SECONDS=600
+MEDIA_MODE=legacy
+MEDIA_PROVIDER=mock
+TURN_URLS=
+TURN_USERNAME=
+TURN_CREDENTIAL=
+MEDIA_RECORDINGS_DIR=media-recordings
+MEDIA_MAX_PUBLISHERS=4
+MEDIA_MAX_SUBSCRIBERS_PER_ROOM=12
 ADMIN_USERNAME=admin
 ADMIN_PASSWORD=strong-password

Backend/README.md

@@ -34,7 +34,11 @@ Required env vars:
 | `BETTER_AUTH_BASE_URL` | Public base URL for the backend (e.g., `http://localhost:3000`) |
 | `BETTER_AUTH_TRUSTED_ORIGINS` | Comma-separated list of allowed frontend origins |
 | `PORT` | HTTP port (default `3000`) |
+| `MEDIA_MODE` | Media runtime mode (`legacy` default, `single_server_sfu` scaffold mode) |
 | `MEDIA_PROVIDER` | Media backend provider (`mock` by default) |
+| `TURN_URLS` / `TURN_USERNAME` / `TURN_CREDENTIAL` | TURN/STUN configuration used by single-server SFU mode |
+| `MEDIA_RECORDINGS_DIR` | Local output directory for server-side recording workers (planned in SFU mode) |
+| `MEDIA_MAX_PUBLISHERS` / `MEDIA_MAX_SUBSCRIBERS_PER_ROOM` | Soft concurrency limits for single-server media mode (planned) |
 | `MINIO_*` | Connection settings for the MinIO/S3 endpoint |
 | `ADMIN_USERNAME` / `ADMIN_PASSWORD` | Basic auth for `/admin` dashboard |
 
@@ -148,6 +152,7 @@ Stream realtime events:
 - Running live transport + fan-out + recording on the same web server is possible for small loads but introduces significant CPU, RAM, and network egress pressure under concurrency.
 - For larger deployments, use a dedicated media plane (managed or self-hosted SFU + recorder) and keep this service focused on auth/session/control APIs.
 - For a pragmatic prototype path that keeps media on the current server, see `docs/streaming-on-web-server-plan.md`.
+- `MEDIA_MODE=single_server_sfu` currently enables scaffolding only (interfaces/config/health visibility), not full SFU media routing yet.
 
 ### API Docs
 OpenAPI docs are generated from Zod/OpenAPI definitions: