feat(input): action maps + deterministic record/replay (#7)

The two ideas the input revamp leads with, built in Ludic over the
single-key poll every target already provides:

- Action maps: gameplay reads named actions, not physical keys, so keys
  are rebindable and a scheme is data. Input.bind(action, key),
  Input.down/pressed(action), Input.rebind(action, from, to).
- Deterministic record/replay: Input.poll() is the one per-frame input
  read; Input.record() captures the key each frame and Input.replay()
  feeds the tape back, so a run reproduces exactly — the seed of lockstep
  netcode. "Read input" and "read a recorded snapshot" are the same call.

runtime/native/input.ludic (spliced when the new Input.* methods are used;
pulls in core.ludic for rt_poll). emit_ns_call routes the methods to the
@fn_input_* runtime; parse.ludic gates the splice. Seven docs/language
pages; worked example + regression examples/library/input_actions.ludic
(1 0 1 1 0 1 0). Full suite 75 passed, self-host fixpoint intact, no golden
drift. The device layer (multi-key held, gamepads, touch, analog) needs a
platform key-state backend and is tracked separately.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/language/input/input-pressed.md

@@ -0,0 +1,24 @@
+---
+id: input-pressed
+name: Input.pressed
+category: input
+kind: namespace-method
+tokens: Input.pressed
+sig: Input.pressed(action: str) -> bool
+tip: Did a named action go down this frame (a one-shot edge)?
+order: 5
+ns: Input
+member: pressed
+---
+
+Returns whether a named action went down <em>this</em> frame — held on the frame last polled, but not on the one before — the edge you want for "press to jump / confirm / fire", where <a href="input-down.html"><code>Input.down</code></a> would retrigger every frame the key is held. Depends on the two most recent <a href="input-poll.html"><code>Input.poll</code></a> calls, so poll once per frame.
+
+```ludic
+program Edge {
+  entry {
+    Input.bind("jump", ' ')
+    Input.poll()
+    if Input.pressed("jump") { print(1) }
+  }
+}
+```