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>

runtime/web/platform.js

@@ -296,6 +296,13 @@ async function start({ wasm, canvas, manifest = null, files = {}, onExit = null,
     },
     win_running: () => host.running,
     win_close: () => { host.running = 0; },
+    // The #50/#51 device-state fills. The browser has no gamepad/touch hardware
+    // wired here yet, so these zero the caller's buffer; keyboard still flows
+    // through win_poll above, and Input.set_* injection works on every target.
+    win_held: (p) => { host.sync(); const b = p >>> 2; for (let i = 0; i < 8; i++) host.u32[b + i] = 0; },
+    win_mouse: (p) => { host.sync(); const b = p >>> 2; for (let i = 0; i < 4; i++) host.u32[b + i] = 0; },
+    win_pad: (p) => { host.sync(); const b = p >>> 2; for (let i = 0; i < 24; i++) host.u32[b + i] = 0; },
+    win_touch: (p) => { host.sync(); const b = p >>> 2; for (let i = 0; i < 24; i++) host.u32[b + i] = 0; },
   };
 
   const { instance } = await WebAssembly.instantiateStreaming(fetch(wasm), { env });