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/0401-protocols-protocol-in-wrapper-struct.sx

@@ -0,0 +1,48 @@
+// Protocol value as a field of a wrapper struct, constructed from a stack
+// local inside a function and appended to a `List`. The payload must be
+// heap-copied so dispatch survives the constructing function returning.
+
+#import "modules/std.sx";
+
+Sizable :: protocol {
+    size :: () -> s64;
+}
+
+Widget :: struct { value: s64; }
+impl Sizable for Widget {
+    size :: (self: *Widget) -> s64 { self.value; }
+}
+
+// Wrapper struct with a protocol field (like ViewChild)
+Item :: struct {
+    view: Sizable;
+}
+
+Container :: struct {
+    items: List(Item);
+
+    add :: (self: *Container, w: Widget) {
+        p := w;  // local copy
+        self.items.append(Item.{ view = p });  // protocol created from stack local `p`
+
+        // Works here: stack local `p` is still alive
+        out("inside add: ");
+        print("{}\n", self.items.items[self.items.len - 1].view.size());
+    }
+}
+
+main :: () -> void {
+    c : Container = .{};
+    c.add(Widget.{ value = 42 });
+    c.add(Widget.{ value = 99 });
+
+    // BUG: items[0] should return 42, but returns 99 (reads items[1]'s stack slot)
+    // Both protocol values point to the same stack address (the `p` local in add())
+    r0 := c.items.items[0].view.size();
+    r1 := c.items.items[1].view.size();
+    print("items[0] = {} (expected 42)\n", r0);
+    print("items[1] = {} (expected 99)\n", r1);
+
+    // With more stack activity between add() and the reads, this crashes
+    // (stack memory overwritten by other function calls)
+}