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/1029-errors-failable-or-chain-propagate.sx

@@ -0,0 +1,21 @@
+// Failable `or` chain propagation (ERR step E2.4b). When every operand of a
+// `try …  or try …` chain fails and there is no value terminator, the final
+// failure propagates to the enclosing function — here `main`, so the E4.2
+// entry-point wrapper prints the unhandled-error header + return trace to
+// stderr and exits 1. Each failed attempt contributes its `raise` frame plus
+// the chain-attempt frame, so three all-failing attempts leave six frames
+// (locations are placeholders until DWARF / E3.0). Expected exit code: 1.
+
+#import "modules/std.sx";
+
+E :: error { A };
+
+fa :: (n: s32) -> (s32, !E) {
+    if n == 0 { raise error.A; }
+    return n;
+}
+
+main :: () -> (s32, !E) {
+    v := try fa(0) or try fa(0) or try fa(0);   // all fail → propagate to main
+    return v;
+}