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/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}`