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/1202-ffi-cc-c-large-aggregate.sx

@@ -0,0 +1,31 @@
+// Regression test for issue-0025 path A.
+//
+// sx functions declared with `callconv(.c)` that take a composite > 16 bytes
+// by value must marshal the arg through `ptr byval(<T>)` per AAPCS64 / SysV
+// AArch64: the caller copies the struct to an alloca, passes the alloca
+// pointer with a `byval(<T>)` attribute, and the callee's entry block loads
+// the struct back from the pointer.
+//
+// Before the fix, abiCoerceParamType returned the raw LLVM struct type for
+// >16-byte composites (TODO at src/ir/emit_llvm.zig:2793), so the C ABI
+// promise was silently violated whenever sx-emitted C-callable code
+// interoperated with a real C caller.
+
+#import "modules/std.sx";
+
+Wide :: struct {
+    a: s64;
+    b: s64;
+    c: s64;
+    d: s64;
+}
+
+accept_c :: (w: Wide) -> s64 callconv(.c) {
+    w.a + w.b + w.c + w.d;
+}
+
+main :: () -> s32 {
+    w := Wide.{ a = 1, b = 10, c = 100, d = 1000 };
+    if accept_c(w) != 1111 { return 1; }
+    0;
+}