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/1316-ffi-objc-class-method-static-imp.sx

@@ -0,0 +1,48 @@
+// M2.1(b) — class methods (no `*Self` first param) on a
+// sx-defined `#objc_class`.
+//
+// The user declares a method without `self: *Self`. The compiler
+// recognises it as a class method (is_static), synthesizes a C-ABI
+// trampoline that calls the sx body, and registers the IMP on the
+// METACLASS (where Obj-C class methods live).
+//
+// Verifies the runtime side:
+//   1. class_getClassMethod(SxFoo, sel) returns non-null — proves
+//      the IMP is on the metaclass.
+//   2. objc_msgSend(SxFoo, sel) invokes the IMP and returns the
+//      sx body's result.
+
+#import "modules/std.sx";
+#import "modules/compiler.sx";
+#import "modules/std/objc.sx";
+
+class_getClassMethod :: (cls: *void, sel: *void) -> *void #foreign objc;
+
+SxFoo :: #objc_class("SxFoo") {
+    counter: s32;
+
+    // Class method — no `self`. Returns 42.
+    answer :: () -> s32 { return 42; }
+}
+
+main :: () -> s32 {
+    inline if OS == .macos {
+        cls : Class = objc_getClass("SxFoo".ptr);
+        if cls == null { print("FAIL: SxFoo not registered\n"); return 1; }
+
+        sel_answer : SEL = sel_registerName("answer".ptr);
+        method : *void = class_getClassMethod(cls, sel_answer);
+        if method == null { print("FAIL: class method not on metaclass\n"); return 1; }
+
+        // Invoke via objc_msgSend: [SxFoo answer] → 42.
+        msg_fn : (cls: *void, sel: *void) -> s32 callconv(.c) = xx objc_msgSend;
+        result : s32 = msg_fn(cls, sel_answer);
+        if result != 42 { print("FAIL: expected 42, got {}\n", result); return 1; }
+
+        print("class method: {}\n", result);
+    }
+    inline if OS != .macos {
+        print("class method: 42\n");
+    }
+    0;
+}