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/0809-memory-xx-lvalue-borrows.sx

@@ -0,0 +1,27 @@
+// Option 3 — `xx <lvalue>` borrows the operand's storage instead of
+// heap-copying. The protocol value's `ctx` points directly at the local;
+// mutations through the protocol are visible to the original.
+//
+// The witness is TrackingAllocator: incrementing the parent allocator's
+// counter happens through the Allocator protocol value. If `xx tracker`
+// heap-copied the Tracker, the parent counter would land in the copy
+// and the local would stay at zero. With Option 3 the local sees the
+// increments because they ARE the local.
+#import "modules/std.sx";
+#import "modules/allocators.sx";
+
+main :: () -> s32 {
+    gpa := GPA.init();
+    tracker := TrackingAllocator.init(xx gpa);   // value, stack-local
+
+    // xx tracker — operand is an identifier (lvalue), so the protocol
+    // borrows tracker's storage. No heap copy. Mutations propagate.
+    push Context.{ allocator = xx tracker, data = null } {
+        p := context.allocator.alloc(128);
+        context.allocator.dealloc(p);
+    }
+
+    print("alloc_count   = {}\n", tracker.alloc_count);
+    print("dealloc_count = {}\n", tracker.dealloc_count);
+    return 0;
+}