ios + ir cleanup

- ios: --target ios/ios-sim shorthands, iOS SDK auto-discovery,
  #framework directive + BuildOptions.add_framework hook,
  .app bundle + Info.plist + codesign (ad-hoc and real),
  --codesign-identity/--provisioning-profile/--entitlements flags,
  modules/std/{objc,uikit}.sx, dynamic class registration,
  typed objc_msgSend cast pattern, UIApplicationMain handoff,
  UIWindow scene attach. Runs on iPhone hardware.
- ir: silent .s64 defaults → loud diagnostics,
  resolveReturnType infers from body, sub-byte int sizes match LLVM,
  tuple type interning includes names, compile errors exit 1
- issue-NNNN convention: resolved bugs rename to focused features
- 50 regression tests passing

examples/53-callconv-c-callbacks.sx

@@ -0,0 +1,16 @@
+// `callconv(.c)` on function pointers passed to foreign callbacks — ensures
+// the function uses C ABI so it can be safely invoked from `#foreign`
+// functions like SDL_AddEventWatch.
+
+#import "modules/std.sx";
+
+// A function with C calling convention
+add_c :: (a: s64, b: s64) -> s64 callconv(.c) {
+    a + b;
+}
+
+main :: () {
+    // Call it directly — should work like any other function
+    result := add_c(10, 32);
+    print("callconv(.c): {}\n", result);
+}