test: group examples into per-category folders

Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.

examples/ffi/1211-ffi-03-large-struct.c

@@ -0,0 +1,30 @@
+#include "1211-ffi-03-large-struct.h"
+
+Big24 ffi_big24_make(long long a, long long b, long long c) {
+    Big24 r = { a, b, c };
+    return r;
+}
+
+Big24 ffi_big24_rotate(Big24 v) {
+    Big24 r = { v.c, v.a, v.b };
+    return r;
+}
+
+long long ffi_big24_sum(Big24 v) {
+    return v.a + v.b + v.c;
+}
+
+Big48 ffi_big48_make(long long a, long long b, long long c,
+                     long long d, long long e, long long f) {
+    Big48 r = { a, b, c, d, e, f };
+    return r;
+}
+
+Big48 ffi_big48_reverse(Big48 v) {
+    Big48 r = { v.f, v.e, v.d, v.c, v.b, v.a };
+    return r;
+}
+
+long long ffi_big48_sum(Big48 v) {
+    return v.a + v.b + v.c + v.d + v.e + v.f;
+}