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/1212-ffi-04-fp-struct.c

@@ -0,0 +1,29 @@
+#include "1212-ffi-04-fp-struct.h"
+
+FQuad ffi_fquad_make(float a, float b, float c, float d) {
+    FQuad r = { a, b, c, d };
+    return r;
+}
+
+FQuad ffi_fquad_reverse(FQuad v) {
+    FQuad r = { v.d, v.c, v.b, v.a };
+    return r;
+}
+
+float ffi_fquad_sum(FQuad v) {
+    return v.a + v.b + v.c + v.d;
+}
+
+DQuad ffi_dquad_make(double a, double b, double c, double d) {
+    DQuad r = { a, b, c, d };
+    return r;
+}
+
+DQuad ffi_dquad_reverse(DQuad v) {
+    DQuad r = { v.d, v.c, v.b, v.a };
+    return r;
+}
+
+double ffi_dquad_sum(DQuad v) {
+    return v.a + v.b + v.c + v.d;
+}