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/0024-basic-for-list.sx

@@ -0,0 +1,40 @@
+// `for` over a `List(T)` (a `{ items: [*]T, len, cap }` struct): value capture,
+// by-ref capture (mutates in place), iterating a `*List`, and a by-ref capture
+// used as a value-receiver method call (auto-deref).
+#import "modules/std.sx";
+
+Box :: struct {
+    v: s64;
+    boxed :: (self: Box) -> s64 { self.v; }   // value receiver
+}
+
+sum_ptr :: (xs: *List(s64)) -> s64 {
+    total : s64 = 0;
+    for xs: (n) { total = total + n; }         // iterate through a *List
+    total;
+}
+
+main :: () -> s32 {
+    xs := List(s64).{};
+    xs.append(10);
+    xs.append(20);
+    xs.append(30);
+
+    s : s64 = 0;
+    for xs: (n) { s = s + n; }                 // value capture
+    print("sum {}\n", s);                      // 60
+
+    for xs: (*n) { n.* = n + 100; }            // by-ref: writes back
+    s = 0;
+    for xs: (n) { s = s + n; }
+    print("sum2 {}\n", s);                     // 360
+
+    print("via ptr {}\n", sum_ptr(@xs));       // 360
+
+    bs := List(Box).{};
+    bs.append(.{ v = 7 });
+    bt : s64 = 0;
+    for bs: (*b) { bt = bt + b.boxed(); }      // *Box receiver, value-self method
+    print("boxes {}\n", bt);                   // 7
+    0;
+}