Native iPhone port of Factorio 2.0.77

Run the original macOS ARM64 game code on iOS:
- tools/retarget.py: header-only Mach-O retargeting to an iOS dylib
- platform/native: UIKit host and macOS API shims (AppKit for SDL's
  Cocoa backend, CoreGraphics displays, CoreAudio device, Metal device
  properties, Wuffs PNG decoding, Steam and peripheral stubs)
- touch, overlay, iOS keyboard and hardware keyboard input
- tools/build_native.py: build, sign, install, data copy, launch
- docs: build guide, controls, architecture

Also includes the earlier static-translation research (ARM64 -> WASM ->
native) under docs/research, runtime/, tests/ and tools/.

No game files are included; the build reads them from a local install.

runtime/save_layout.h

@@ -0,0 +1,18 @@
+#ifndef FACTORIO_SAVE_LAYOUT_H
+#define FACTORIO_SAVE_LAYOUT_H
+#include "save_header.h"
+#include "map_header_bridge.h"
+
+/* Bounded host reconstruction of the 2.0.77 base-game scenario envelope.
+ * Only empty startup PropertyTree settings are currently supported.
+ * This locates MapHeader; it does not initialize a Scenario or load a world. */
+typedef struct {
+  FactorioMapHeader header;
+  size_t header_offset, next_offset;
+  uint32_t mod_count;
+} FactorioSaveLayout;
+int factorio_save_layout_bytes(const uint8_t *prefix, size_t length,
+                              FactorioSaveLayout *out, size_t *needed);
+int factorio_save_map_header(const char *path, FactorioSaveLayout *out);
+const char *factorio_save_layout_status_string(int status);
+#endif