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>

selfhost/frontend/parse.ludic

@@ -189,7 +189,7 @@ function p_postfix() -> Node {
       if e.a.kind == E_ID and e.a.s == "Reflect" and (e.s == "serialize" or e.s == "apply") { g_uses_value = true;  g_uses_reflect_io = true }   # Reflect.serialize/apply -> value tree + world table
       # Input.* action-map / record-replay methods (#7) -> splice input.ludic.
       # Input.key stays bare (no runtime), so gate on the new methods only.
-      if e.a.kind == E_ID and e.a.s == "Input" and (e.s == "bind" or e.s == "rebind" or e.s == "poll" or e.s == "down" or e.s == "pressed" or e.s == "record" or e.s == "replay") { g_uses_input = true }
+      if e.a.kind == E_ID and e.a.s == "Input" and (e.s == "bind" or e.s == "rebind" or e.s == "poll" or e.s == "down" or e.s == "pressed" or e.s == "record" or e.s == "replay" or e.s == "action" or e.s == "bind_pad" or e.s == "active" or e.s == "just_pressed" or e.s == "just_released") { g_uses_input = true }
       # #50 device layer — any of the multi-key / analog / mouse / gamepad / touch
       # methods also splices input.ludic (Input.key stays bare, no runtime).
       if e.a.kind == E_ID and e.a.s == "Input" and (e.s == "key_down" or e.s == "key_pressed" or e.s == "key_released" or e.s == "press" or e.s == "release" or e.s == "axis" or e.s == "vector" or e.s == "strength" or e.s == "mouse_x" or e.s == "mouse_y" or e.s == "mouse_dx" or e.s == "mouse_dy" or e.s == "mouse_down" or e.s == "wheel" or e.s == "set_mouse" or e.s == "pad_connected" or e.s == "pad_button" or e.s == "pad_axis" or e.s == "set_pad" or e.s == "touch_count" or e.s == "touch_x" or e.s == "touch_y" or e.s == "set_touch") { g_uses_input = true }