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.

tests/save_layout_native.c

@@ -0,0 +1,37 @@
+#include "save_layout.h"
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+  const uint8_t *bytes;
+  size_t length,cursor;
+  uint64_t version[2];
+  unsigned reads;
+} NativeReader;
+extern void *factorio_map_header_original(void *,NativeReader *);
+void native_map_header_read(NativeReader *r,void *out,size_t size) {
+  assert(size==8 && r->reads<3 && r->cursor+size<=r->length);
+  memcpy(out,r->bytes+r->cursor,size);r->cursor+=size;++r->reads;
+}
+int main(int argc,char **argv) {
+  if(argc!=2) return 2;
+  FactorioSaveLayout layout;
+  assert(factorio_save_map_header(argv[1],&layout)==0);
+  uint8_t *prefix=malloc(layout.next_offset);assert(prefix);
+  assert(factorio_save_prefix(argv[1],prefix,layout.next_offset)==0);
+  FactorioMapVersion v=layout.header.version;
+  NativeReader reader={.bytes=prefix,.length=layout.next_offset,.cursor=layout.header_offset,
+    .version={(uint64_t)v.major<<48|(uint64_t)v.minor<<32|(uint64_t)v.patch<<16|v.build,v.flag}};
+  uint8_t native[48];memset(native,0xa5,sizeof(native));
+  assert(factorio_map_header_original(native,&reader)==native);
+  assert(reader.reads==3 && reader.cursor==layout.next_offset);
+  assert(memcmp(native+16,layout.header.tick_fields,24)==0);
+  for(unsigned i=40;i<48;++i) assert(native[i]==0xa5);
+  free(prefix);
+  printf("{\"status\":\"pass\",\"header_offset\":%zu,\"native_reads\":%u,"
+    "\"constructor_values_match\":true,\"offset_authority\":\"recovered metadata layout; not full-engine execution\"}\n",
+    layout.header_offset,reader.reads);
+  return 0;
+}