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/1005-errors-try-rejections.sx

@@ -0,0 +1,41 @@
+// `try` rejections (ERR step E1.4a):
+//   - `try` is only valid inside a failable function,
+//   - the operand must be failable (the sole failable-operand check —
+//     the parser imposes none),
+//   - propagating a `try` whose callee's error set is not a subset of the
+//     caller's named set is rejected (widening at a function-propagation site).
+// The positive case lives in `examples/221-try.sx`.
+
+#import "modules/std.sx";
+
+A :: error { Xa }
+B :: error { Yb }
+
+ga    :: () -> !A  { return; }
+gb    :: () -> !B  { return; }
+plain :: () -> s32 { return 0; }
+
+// `try` in a non-failable function.
+bad_ctx :: () -> s32 {
+    try ga();                  // error: `try` outside a failable function
+    return 0;
+}
+
+// `try` on a non-failable operand.
+bad_operand :: () -> !A {
+    try plain();               // error: operand has type s32 (not failable)
+    return;
+}
+
+// Callee's set (B = {Yb}) is not a subset of the caller's set (A = {Xa}).
+widen :: () -> !A {
+    try gb();                  // error: Yb not in caller's error set A
+    return;
+}
+
+main :: () -> s32 {
+    a := bad_ctx();            // force bad_ctx to lower
+    b := bad_operand();        // force bad_operand to lower
+    c := widen();              // force widen to lower
+    return 0;
+}