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/1307-ffi-objc-expression-bodied-objc-method.sx

@@ -0,0 +1,20 @@
+// M1.0 (xfail) — '=>' expression-body form inside '#objc_class'
+// member methods.
+//
+// Today: parseForeignClassDecl ([src/parser.zig:1262]) accepts ';'
+// (declaration) or '{ ... }' (block body) but not '=>'. Trying
+// '=>' surfaces 'expected ;' at the arrow.
+//
+// Next commit extends the member parser to accept the arrow
+// form, mirroring the existing parseFnDecl ('=>') arm, and this
+// snapshot flips from a parser error to '42\n'.
+
+#import "modules/std.sx";
+
+SxFoo :: #objc_class("SxFoo") {
+    greet :: (self: *Self) -> s32 => 42;
+}
+
+main :: () -> s32 {
+    0;
+}