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/0530-packs-pack-interface-only.sx

@@ -0,0 +1,22 @@
+// Feature 1 — a pack element exposes ONLY the constraint protocol's interface.
+// `xs[i].v` reaches a concrete field of IntCell that is not part of `Box`, so
+// it's rejected even though IntCell does have `v` — a pack element is viewed
+// through the protocol, like a constrained generic. (Protocol methods like
+// `get()` ARE callable; see examples 193/194.)
+
+#import "modules/std.sx";
+
+Box :: protocol(T: Type) {
+    get :: () -> T;
+}
+IntCell :: struct { v: s64; }
+impl Box(s64) for IntCell { get :: (self: *IntCell) -> s64 => self.v; }
+
+leak :: (..xs: Box) -> s64 {
+    return xs[0].v;   // `v` is not part of Box — error
+}
+
+main :: () -> s32 {
+    print("{}\n", leak(IntCell.{ v = 5 }));
+    0;
+}