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/0707-modules-import-dir-scan-order/aaa_uses.sx

@@ -0,0 +1,11 @@
+// Alphabetically FIRST file in the directory. Its own decl uses
+// `MyEnum`, defined in a sibling file (`types.sx`). The directory
+// import pass must register `MyEnum` BEFORE this file's `make_my`
+// is scanned, or `MyEnum` falls back to a placeholder struct and
+// `return .b(42)` fails with "cannot infer enum type".
+
+#import "types.sx";
+
+make_my :: () -> MyEnum {
+    return .b(42);
+}

examples/0707-modules-import-dir-scan-order/types.sx

@@ -0,0 +1,4 @@
+MyEnum :: enum {
+    a;
+    b: s32;
+}