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/55-err-field-not-found.sx

@@ -0,0 +1,9 @@
+// Accessing an unknown field on a struct produces a clear
+// `error: field 'X' not found on type 'Y'` diagnostic and exit 1.
+
+Vec :: struct { x: f32; y: f32; }
+
+main :: () -> s32 {
+    v := Vec.{ x = 1.0, y = 2.0 };
+    return xx v.bogus;
+}