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/0402-protocols-protocol-list-from-fn.sx

@@ -0,0 +1,42 @@
+// `List(Protocol)` appended from inside a helper function, dispatched
+// repeatedly from `main` after the helper returns. Exercises the heap-copy
+// path for both implicit-erasure-on-append and pre-erased protocol values.
+
+#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);  // protocol value created from stack local `p`
+}
+
+main :: () -> void {
+    // Works: protocol value created in main, appended to list
+    out("=== Created in main ===\n");
+    list_a : List(Sizable) = .{};
+    s : Sizable = Leaf.{ value = 42 };
+    list_a.append(s);
+    r1 := list_a.items[0].size();
+    print("first:  {} (expected 42)\n", r1);
+    r2 := list_a.items[0].size();
+    print("second: {} (expected 42)\n", r2);
+
+    // BUG: protocol value created in add(), first dispatch works, second crashes
+    out("=== Created in add() ===\n");
+    list_b : List(Sizable) = .{};
+    add(@list_b, Leaf.{ value = 99 });
+    r3 := list_b.items[0].size();
+    print("first:  {} (expected 99)\n", r3);   // works (stack not yet clobbered)
+    r4 := list_b.items[0].size();
+    print("second: {} (expected 99)\n", r4);   // CRASH: stack memory reused
+
+    out("=== OK ===\n");
+}