fix(input): #87 key_pressed/key_released edges never fired under the frame loop

Since #83 the loop commits the device layer once per frame (input_drive), but a
game that ALSO called Input.poll by hand committed a second time in the same
frame; input_device_commit copies in_held into in_prev at the top of every
commit, so the second commit left in_prev == in_held and the edges (held &&
!prev) could never see a transition.

Fix: an in_have_frame_driver flag. The loop's input_drive sets it; a manual
Input.poll under the loop then becomes a no-op returning the frame's key
instead of re-committing. An entry-driven harness has no loop, so the flag
stays false and each Input.poll commits a frame as before (the #7/#50
record/replay + device tests are unchanged). Frame loop now calls input_drive.

Example input_edge (press edge on the down frame, release edge on the up
frame). Full suite 110/0, goldens byte-identical, fixpoint holds.

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

examples/library/input_edge.ludic

@@ -0,0 +1,27 @@
+# input_edge.ludic — Input.key_pressed / key_released edge detection (#87). A
+# handler game reads the press and release edges of a key in its Update phase; the
+# frame loop commits the device layer itself (#83), so the game does NOT call
+# Input.poll by hand, and the edges fire on exactly the transition frame. (The bug:
+# a manual Input.poll under the loop used to double-commit and copy in_held into
+# in_prev twice, so key_pressed/key_released never fired.)
+#
+# Driven headless by the keys on stdin, one char per frame. With "xkkxq":
+#   x   frame0 — nothing
+#   k   frame1 — pressed edge (down + just went down)
+#   k   frame2 — held (down, no edge)
+#   x   frame3 — released edge (was k, now not)
+#   q   frame4 — nothing, then quit
+#
+# Run:  printf 'xkkxq' | bin/ludic examples/library/input_edge.ludic   ->  0 11 1 100 0
+program InputEdge {
+  property Tag { n: int = 0 }
+  model P { Tag }
+
+  handler In phase Update {
+    var v = 0
+    if Input.key_down('k')     { v = v + 1 }       # held
+    if Input.key_pressed('k')  { v = v + 10 }      # went down this frame
+    if Input.key_released('k') { v = v + 100 }     # went up this frame
+    print(v)
+  }
+}