feat(input): #83 Input Manager + auto-commit the device layer in the frame loop

Fixes the papercut: the generated frame loop called rt_poll() (feeding only
Input.key) but never input_poll(), so Input.active/key_down/mouse/pad read
empty unless the game called Input.poll() by hand. The loop now calls
input_poll() when the game uses any Input runtime method — committing the
held-key/mouse/gamepad state, and record/replay — and stores its return as the
frame key so Input.key still works. A game using no Input runtime keeps the
plain rt_poll path, byte-identical.

Adds the Input-Manager API: Input.action(name,key) ships a default binding
(kept if already bound, so a rebind/loaded map isn't clobbered),
Input.bind_pad(name,button) makes an action device-agnostic (keyboard OR pad),
and Input.active/just_pressed/just_released read the multi-key device layer
with clean on-press/on-release edges (deterministic, dispatch-free — a handler
polls the edge; a replay fires identically).

Examples input_manager + input_auto, 5 docs pages. Full suite 107/0, goldens
byte-identical, fixpoint holds.

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

docs/language/input/input-bind_pad.md

@@ -0,0 +1,24 @@
+---
+id: input-bind_pad
+name: Input.bind_pad
+category: input
+kind: namespace-method
+tokens: Input.bind_pad
+sig: Input.bind_pad(action: str, button: int) -> void
+tip: Also fire a named action from a gamepad button (device-agnostic).
+order: 32
+ns: Input
+member: bind_pad
+---
+
+Maps a gamepad <code>button</code> (on pad 0) to a named action, so the action fires from the keyboard <em>or</em> the pad. The same action can carry both keyboard keys (<a href="input-bind.html"><code>Input.bind</code></a> / <a href="input-action.html"><code>Input.action</code></a>) and pad buttons; <a href="input-active.html"><code>Input.active</code></a> and its edges fire on either device — one action, any input.
+
+```ludic
+program Pad {
+  entry {
+    Input.action("fire", 'j')
+    Input.bind_pad("fire", 0)
+    if Input.active("fire") { print(1) }
+  }
+}
+```