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/1007-errors-inferred-widening-reject.sx

@@ -0,0 +1,30 @@
+// Inferred-set widening rejection (ERR step E1.4b). When a named caller
+// (`-> !A`) `try`s a bare-`!` callee, the callee's WHOLE-PROGRAM-CONVERGED
+// inferred set must be a subset of A. Before the SCC pass this was a
+// false-negative (the bare-`!` placeholder was empty, so the check trivially
+// passed); now the converged tags are checked. `deep`'s converged set is
+// {Foo} (raised transitively through `via`), which is not in A = {Bar}.
+// The positive case lives in `examples/223-inferred-error-sets.sx`.
+
+#import "modules/std.sx";
+
+A :: error { Bar }
+
+deep :: () -> ! {
+    raise error.Foo;                 // deep's inferred set = {Foo}
+}
+
+via :: () -> ! {
+    try deep();                      // via absorbs {Foo}
+    return;
+}
+
+caller :: () -> !A {
+    try via();                       // error: Foo (via's converged set) not in A
+    return;
+}
+
+main :: () -> s32 {
+    e := caller();
+    return 0;
+}