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_header.h

@@ -0,0 +1,15 @@
+#ifndef FACTORIO_SAVE_HEADER_H
+#define FACTORIO_SAVE_HEADER_H
+#include "version_bridge.h"
+
+/* Header probe only: does not verify the whole archive or deserialize the map. */
+enum FactorioSaveStatus { FACTORIO_SAVE_OK = 0, FACTORIO_SAVE_IO,
+  FACTORIO_SAVE_INVALID_ZIP, FACTORIO_SAVE_NO_LEVEL,
+  FACTORIO_SAVE_UNSUPPORTED, FACTORIO_SAVE_COMPRESSION,
+  FACTORIO_SAVE_SHORT_HEADER, FACTORIO_SAVE_PREFIX_LIMIT };
+int factorio_save_header(const char *path, FactorioMapVersion *out);
+/* Decode exactly length bytes of the nested map stream (1..1 MiB).
+ * Writes out only on success. Does not validate the complete stream/archive. */
+int factorio_save_prefix(const char *path, uint8_t *out, size_t length);
+const char *factorio_save_status_string(int status);
+#endif