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/1003-errors-raise-rejections.sx

@@ -0,0 +1,32 @@
+// `raise` rejections (ERR step E1.3):
+//   - `raise` is only valid inside a failable function,
+//   - a literal `raise error.X` must name a tag in the function's set,
+//   - a variable `raise e` must carry a set that is a subset of the
+//     function's set.
+// The positive case lives in `examples/219-raise.sx`. Parse-time rejections
+// (`raise` in expression position / inside `defer` / `onfail`) are covered by
+// the inline parser tests.
+
+#import "modules/std.sx";
+
+ParseErr :: error { BadDigit, Overflow }
+OtherErr :: error { Weird }
+
+// Literal tag not in the declared set.
+bad_tag :: () -> !ParseErr {
+    raise error.NotInSet;            // error: NotInSet not in ParseErr
+}
+
+// Variable whose error set is not a subset of the function's set.
+makes_other :: () -> !OtherErr { return; }
+relay :: () -> !ParseErr {
+    e := makes_other();              // e : OtherErr
+    raise e;                         // error: OtherErr not subset of ParseErr
+}
+
+main :: () -> s32 {
+    x := bad_tag();                  // force bad_tag to lower
+    y := relay();                    // force relay to lower
+    raise error.BadDigit;            // error: main (-> s32) is not failable
+    return 0;
+}