Refresh README: real WebRTC controller (drop placeholder)

README.md

@@ -1,20 +1,41 @@
 # game-controller
 
-Phone/controller client for **Space Console** — turns a phone into a game
-controller that joins a launcher (the TV) via a short room code, AirConsole-style.
-Pairs with the `game-launcher-web` repo (the TV/screen side).
+The **phone/controller** app for **Space Console** — turns a phone into a game
+controller that joins the launcher (the TV) by a short **room code** or a scanned
+QR, AirConsole-style. Pairs with the `game-launcher-web` repo (the TV/screen side).
+
+It opens a **WebRTC DataChannel straight to the TV** and sends input peer-to-peer;
+the `web-api` service only brokers the handshake (room code + SDP/ICE) and vends
+STUN/TURN. The controller renders whatever pad the running game asks for over that
+channel:
+
+- a **d-pad** + action buttons for menus and classic games;
+- a **landscape analog driving pad** (steering joystick + gas / brake / drift,
+  with optional tilt steering) for racing games, streamed as continuous frames;
+- **name entry** on join (shown in the TV's player roster), and **auto-rejoin**
+  if the tab is backgrounded or the network blips.
 
 Zero-build, zero-backend static site — plain ES modules, no bundler, no
 framework. Open `index.html` and it runs.
 
 ```sh
-npm install     # dev server only
-npm run dev      # http://localhost:5174 (auto-reload)
+npm install     # dev tooling only
+npm run dev     # http://localhost:5174 (auto-reload)
 ```
 
-This is an early **placeholder**: a join screen + a stubbed control pad whose
-transport (`assets/js/session.js connect()/send()`) is a seam to fill in with a
-real WebSocket / WebRTC / AirConsole client.
+## Transport
+
+The client lives in `assets/js/session.js`:
+
+- `send(intent)` — a discrete button press (`up/down/left/right/enter/back`, plus
+  game-declared aux buttons like `reset` / `powerup`).
+- `sendAnalog(steer, throttle, brake, handbrake)` — a continuous driving frame.
+
+Both go over the DataChannel; the TV relays them into the running game. Signaling
+defaults to the page's own origin, and ICE/TURN is fetched from the server at
+`/api/ice` (a `?signal=` / `?turn=` query param can override per device). For real
+phones, the controller, the launcher and the signaling socket must share **one
+origin** — the `web-api` repo serves them together (see its README).
 
 ## Documentation