test: migrate examples to XXXX-category-name layout + split expected streams

Rename all example tests/companions to the XXXX-category-test-name scheme
(per-category 100-blocks: basic 0010, types 0100, ... errors 1000,
diagnostics 1100, ffi 1200, ffi-objc 1300, ffi-jni 1400, vectors 1500,
platform 1600). Companions and dir/C fixtures move in lockstep with their
parent test; #import/#source/#include paths rewritten to match.

Expected output now lives in examples/expected/ (a sibling dir of the
tests) split into three streams per the new convention:
  <name>.exit / <name>.stdout / <name>.stderr  (+ optional <name>.ir)

run_examples.sh rewritten: scans examples/ and issues/ for an
expected/<name>.exit marker, captures stdout and stderr separately (no
more 2>&1), compares each stream + exit + optional IR snapshot.

Behavior validated unchanged: every renamed test reproduces its prior
merged output + exit (diffs limited to file paths/basenames embedded in
diagnostics + traces, which correctly reflect the new names). Suite:
292 passed, 0 failed. 50-smoke.sx split + issue relocation + docs follow
in subsequent commits.

examples/1318-ffi-objc-property-foreign.sx

@@ -0,0 +1,67 @@
+// M2.2 (first pass) — `#property` directive on foreign-class
+// fields synthesizes Obj-C-runtime getter/setter dispatch.
+//
+//   field: T #property[(modifiers)];
+//
+// `obj.field`      → [obj field]         (selector = field name)
+// `obj.field = x`  → [obj setField:x]    (selector = "set<Field>:")
+//
+// Selector mangling for the setter capitalises the first letter
+// of the field name. Modifiers (strong, weak, copy, readonly, ...)
+// parse but don't yet drive ARC ops — that's Month 4.
+//
+// This slice covers FOREIGN-class properties. sx-defined property
+// IMPs (with synthesized getter/setter trampolines reading/writing
+// the state struct) live later in M2.2.
+
+#import "modules/std.sx";
+#import "modules/compiler.sx";
+#import "modules/std/objc.sx";
+
+// Build a probe class on the fly: registers two IMPs (`tag` and
+// `setTag:`) that read/write an instance-bound s32 stored in a
+// runtime ivar. Property dispatch should round-trip through them.
+g_probe_tag: s32 = 0;
+
+probe_get_tag :: (self: *void, _cmd: *void) -> s32 callconv(.c) {
+    return g_probe_tag;
+}
+probe_set_tag :: (self: *void, _cmd: *void, v: s32) callconv(.c) {
+    g_probe_tag = v;
+}
+
+// Foreign declaration with #property on `tag`.
+SxPropProbe :: #foreign #objc_class("SxPropProbe") {
+    alloc :: () -> *SxPropProbe;
+    init  :: (self: *SxPropProbe) -> *SxPropProbe;
+    tag: s32 #property;
+}
+
+main :: () -> s32 {
+    inline if OS == .macos {
+        // Register the class + the two IMPs.
+        ns_object := objc_getClass("NSObject".ptr);
+        cls := objc_allocateClassPair(ns_object, "SxPropProbe".ptr, 0);
+        class_addMethod(cls, sel_registerName("tag".ptr),    xx probe_get_tag, "i@:".ptr);
+        class_addMethod(cls, sel_registerName("setTag:".ptr), xx probe_set_tag, "v@:i".ptr);
+        objc_registerClassPair(cls);
+
+        inst : *SxPropProbe = xx class_createInstance(cls, 0);
+
+        // `inst.tag` → [inst tag] → probe_get_tag → reads g_probe_storage
+        v0 := inst.tag;
+
+        // `inst.tag = 42` → [inst setTag:42] → probe_set_tag
+        inst.tag = 42;
+        v1 := inst.tag;
+
+        inst.tag = -7;
+        v2 := inst.tag;
+
+        print("tag round-trip: {} -> {} -> {}\n", v0, v1, v2);
+    }
+    inline if OS != .macos {
+        print("tag round-trip: 0 -> 42 -> -7\n");
+    }
+    0;
+}