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>

tools/x/build.ludic

@@ -77,7 +77,7 @@ function cmd_app() -> int {
   let ll = `{outbin}.ll`
   print(`ludicc: {src} -> {outbin}  (Ludic-written compiler -> LLVM IR -> windowed binary)`)
   if not shq(`bin/ludicc --windowed {src} > {ll}`) { return 1 }
-  if not shq(`{cc()} -O2 {ll} runtime/native/cocoa.ll -framework Cocoa -Wl,-rpath,@loader_path -o {outbin}`) { return 1 }
+  if not shq(`{cc()} -O2 {ll} runtime/native/cocoa.ll -framework Cocoa -Wl,-needed_framework,GameController -Wl,-rpath,@loader_path -o {outbin}`) { return 1 }
   if not save { run(`rm -f {ll}`) }
   print(`done. run: ./{outbin}   (from the repo root, so assets/ resolves)`)
   return 0