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/0403-protocols-protocol-dispatch-via-fn-arg.sx

@@ -0,0 +1,44 @@
+// Protocol dispatch on `List(Protocol)` items where the list pointer is
+// passed into another function — verifies the boxed payload survives an
+// extra call frame between erasure and dispatch.
+
+#import "modules/std.sx";
+
+Sizable :: protocol {
+    size :: () -> s64;
+}
+
+Leaf :: struct { value: s64; }
+impl Sizable for Leaf {
+    size :: (self: *Leaf) -> s64 { self.value; }
+}
+
+add :: (items: *List(Sizable), w: Leaf) {
+    p := w;
+    items.append(p);
+}
+
+dispatch_fn :: (items: *List(Sizable)) {
+    out("dispatch_fn: about to dispatch\n");
+    s := items.items[0].size();
+    print("dispatch_fn: result = {}\n", s);
+}
+
+main :: () -> void {
+    items : List(Sizable) = .{};
+    add(@items, Leaf.{ value = 42 });
+
+    // Direct dispatch twice
+    out("=== Direct 1 ===\n");
+    r1 := items.items[0].size();
+    print("r1 = {}\n", r1);
+
+    out("=== Direct 2 ===\n");
+    r2 := items.items[0].size();
+    print("r2 = {}\n", r2);
+
+    // Then from function
+    out("=== From function ===\n");
+    dispatch_fn(@items);
+    out("=== OK ===\n");
+}