feat(fsharp): m11 pong capstone (model, rules, view, app) with tests

Co-Authored-By: Claude Opus 5.5 <[email protected]>

fsharp/src/Pong/App.fs

@@ -0,0 +1,29 @@
+/// m11 pong app: the same wiring as App.fs (streams in, drawings out), reusing the course's modules.
+module Snake.Pong.App
+
+open Snake
+open Snake.IO
+open Snake.Stream
+open Snake.Pong.Model
+open Snake.Pong.Rules
+open Snake.Pong.View
+
+/// Milliseconds between frames of the match.
+let FRAME_MS_PONG = 30L
+
+/// Translate a key event into a `PongAction`, if any. `isDown` is true for a key press, false for a release.
+/// "ArrowUp"/"w"/"W" -> `Press Paddle.Up` / `Release Paddle.Up`, "ArrowDown"/"s"/"S" -> `Press Paddle.Down` /
+/// `Release Paddle.Down`, "r"/"R" -> `Restart` (on press only; releasing r does nothing). Any other key -> `None`.
+let pongKey (isDown: bool) (key: string) : PongAction option = failwith "TODO m11"
+
+/// Everything that can happen in a match: `Frame` every FRAME_MS_PONG (from `Stream.interval`), merged with the
+/// `pongKey true key` of every key press and the `pongKey false key` of every key release.
+/// (The stub is wrapped in `Stream` so the TODO only fires when the stream is stepped.)
+let pongActions: Stream<PongAction> = Stream(fun _ -> failwith "TODO m11")
+
+/// Fold the actions into a stream of states: start from `initialPong seed`, `pongUpdate` for each action, emit the initial state first.
+let pongStates (seed: uint32) (actions: Stream<PongAction>) : Stream<PongState> = failwith "TODO m11"
+
+/// The whole program as a value, like `App.main`: ask for a seed, turn the stream of states into a stream of drawings
+/// of `pongView`. A function of `unit`, like `App.main`.
+let pongMain () : IO<Stream<IO<unit>>> = failwith "TODO m11"