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/1309-ffi-objc-class-method-lowering.sx

@@ -0,0 +1,42 @@
+// M1.2 A.2c / A.3 — instance-method body lowering on sx-defined
+// `#objc_class`.
+//
+// The Obj-C runtime invokes class methods via the IMP pointers
+// wired up in M1.2 A.4. No sx-side call path drives lazy lowering,
+// so the eager pass `lowerObjcDefinedClassMethods` walks the
+// `objc_defined_class_cache` and force-lowers every bodied method
+// after Pass 1 finishes.
+//
+// `*Self` substitution (A.2b) routes the param's pointee type to
+// the hidden state-struct `__<ClassName>State`. `self.counter`
+// then resolves as a plain struct field access — A.3's "free if
+// types align". The IR snapshot pins the round-trip:
+//
+//   define internal void @SxFoo.bump(ptr __sx_ctx, ptr self) {
+//       %gep = getelementptr inbounds { i32 }, ptr %self, 0, 0
+//       %v = load i32, ptr %gep
+//       %inc = add i32 %v, 1
+//       store i32 %inc, ptr %gep
+//       ret void
+//   }
+//
+// IMP-trampoline emission (the C-ABI shim that the Obj-C runtime
+// calls and that reads the `__sx_state` ivar) lands separately
+// in M1.2 A.4 alongside class-pair init. Runtime dispatch
+// (M1.2 A.7) stays gated until then.
+
+#import "modules/std.sx";
+#import "modules/compiler.sx";
+
+SxFoo :: #objc_class("SxFoo") {
+    counter: s32;
+
+    bump :: (self: *Self) {
+        self.counter += 1;
+    }
+}
+
+main :: () -> s32 {
+    print("compiled\n");
+    0;
+}