feat(input): native gamepad + touch + mouse-position hardware bindings (#51)

Wire the macOS platform side of the #50 device layer, feeding the same state
buffers the read APIs consume — no API changes, purely OS glue.

- mouse: cocoa.ll reads the live cursor via mouseLocationOutsideOfEventStream,
  converted to framebuffer pixels and y-flipped, so windowed games get
  Input.mouse_x/y without injection (W_mx/W_my were never written before).
- gamepad: win_pad polls GCController.controllers each frame, packing extended-
  gamepad buttons (SDL_GameControllerButton order) and thumbsticks (16.16 fixed,
  Y negated for SDL convention) into in_pad_*. Windowed builds now load
  GameController via -needed_framework (its classes are reached by name, so a
  plain -framework link dead-strips it); DCE'd in headless builds.
- touch: the view's NSTouch phase handlers snapshot the touching set into
  in_touch_* (normalizedPosition -> framebuffer pixels).

Web platform.js gains zero-fill stubs for win_held/mouse/pad/touch so a windowed
wasm build resolves the device-layer imports. New test asserts the windowed link
loads GameController. Reseeded; full + selfhost suites green (79 + 29).

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

selfhost/backend/emit_head.ludic

@@ -65,6 +65,8 @@ function emit_header() -> void {
   emith("declare void @win_close()\n")
   emith("declare void @win_held(ptr)\n")
   emith("declare void @win_mouse(ptr)\n")
+  emith("declare void @win_pad(ptr)\n")
+  emith("declare void @win_touch(ptr)\n")
   emith("@__stderrp = external global ptr\n")
   emith("@__stdoutp = external global ptr\n")
   emith("@.fmt_int = private unnamed_addr constant [4 x i8] c\"%d\\0A\\00\"\n")

selfhost/backend/emit_intrin2.ludic

@@ -12,6 +12,7 @@ function is_intrinsic2(name: pointer) -> bool {
   if (name == "win_open") or (name == "win_poll") or (name == "win_present") { return true }
   if (name == "win_running") or (name == "win_close") { return true }
   if (name == "win_held") or (name == "win_mouse") { return true }   # #50 device layer
+  if (name == "win_pad") or (name == "win_touch") { return true }    # #51 gamepad / touch
   return false
 }
 
@@ -55,5 +56,9 @@ function emit_intrinsic2(name: pointer, e: Node) -> Val {
   # button-mask, wheel-delta].
   if (name == "win_held")  { let a = arg_code(e, 0);  emit("  call void @win_held(ptr ");  emit(a);  emit(")\n");  return val("0", "void") }
   if (name == "win_mouse") { let a = arg_code(e, 0);  emit("  call void @win_mouse(ptr ");  emit(a);  emit(")\n");  return val("0", "void") }
+  # #51 — win_pad: 6 words/pad [connected, mask, lx, ly, rx, ry]; win_touch: 3
+  # words/point [active, x, y]. Both windowed-only, DCE'd headless.
+  if (name == "win_pad")   { let a = arg_code(e, 0);  emit("  call void @win_pad(ptr ");  emit(a);  emit(")\n");  return val("0", "void") }
+  if (name == "win_touch") { let a = arg_code(e, 0);  emit("  call void @win_touch(ptr ");  emit(a);  emit(")\n");  return val("0", "void") }
   return val("0", "void")
 }

selfhost/main.ludic

@@ -160,7 +160,11 @@ entry {
   var cmd = `{cc} -O2 -Wno-override-module {ll}`
   if g_windowed {
     let cocoa = path_join(home, "runtime/native/cocoa.ll")
-    cmd = `{cmd} {cocoa} -framework Cocoa -Wl,-rpath,@loader_path`
+    # GameController holds no symbol cocoa.ll references directly (its classes are
+    # reached by name through objc_getClass), so a plain -framework link gets
+    # dead-stripped; -needed_framework forces the load command so the class is
+    # registered and #51's gamepad polling can see it.
+    cmd = `{cmd} {cocoa} -framework Cocoa -Wl,-needed_framework,GameController -Wl,-rpath,@loader_path`
   }
   cmd = `{cmd} -o {out}`