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>

examples/library/input_auto.ludic

@@ -0,0 +1,20 @@
+# input_auto.ludic — proves the frame loop commits the device layer automatically
+# (#83): a real handler game reads Input.active in its Update phase and NEVER calls
+# Input.poll by hand, yet the action fires from the live key. Before this fix the
+# loop only fed Input.key(), so Input.active read empty unless the game polled.
+#
+# Driven headless by the keys on stdin — one char per frame. With "llq": frame 1
+# and 2 read 'l' (the action key), frame 3 reads 'q' (which quits). So the action
+# is active on exactly two frames.
+#
+# Run:  printf 'llq' | bin/ludic examples/library/input_auto.ludic   ->  2
+program InputAuto {
+  property Tag { n: int = 0 }
+  model Player { Tag }
+
+  var hits: int = 0
+
+  @OnStart handler Boot { Input.action("go", 'l') }        # 'l' == 108
+  handler Sense phase Update { if Input.active("go") { hits = hits + 1 } }
+  @OnQuit handler Report { print(hits) }
+}