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>

selfhost/backend/emit_call.ludic

@@ -177,6 +177,15 @@ function emit_ns_call(ns: pointer, meth: pointer, e: Node) -> Val {
   }
   if (ns == "Input") {
     if (meth == "key") { bare = "key" }
+    # action maps + deterministic record/replay (#7) — spliced runtime in
+    # runtime/native/input.ludic, reached as ordinary @fn_input_* calls.
+    if (meth == "bind")    { bare = "input_bind" }
+    if (meth == "rebind")  { bare = "input_rebind" }
+    if (meth == "poll")    { bare = "input_poll" }
+    if (meth == "down")    { bare = "input_down" }
+    if (meth == "pressed") { bare = "input_pressed" }
+    if (meth == "record")  { bare = "input_record" }
+    if (meth == "replay")  { bare = "input_replay" }
   }
   # Phase 3: the bare reflection / networking / process builtins, namespaced.
   # Each is a pure alias — the callee is rewritten to the bare name below.