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/0411-protocols-impl-duplicate.sx

@@ -0,0 +1,23 @@
+// Duplicate impl detection — two impls for the same (Source, Target)
+// pair are both visible from the same `xx` site (because both their
+// defining modules are transitively imported). The compiler must
+// emit a "duplicate xx conversion" diagnostic naming both modules,
+// not silently pick one or the other.
+//
+// Setup:
+//   - 180-impl-duplicate-impl-a.sx: `impl Into(Wrap) for s64` (mul by 10).
+//   - 180-impl-duplicate-impl-b.sx: `impl Into(Wrap) for s64` (add 100).
+//   - Main imports both; the `xx 7 : Wrap` site must error.
+//
+// Expected exit = 1, expected output = the focused diagnostic naming
+// both impl modules.
+
+#import "modules/std.sx";
+#import "./0411-protocols-impl-duplicate-impl-a.sx";
+#import "./0411-protocols-impl-duplicate-impl-b.sx";
+
+main :: () -> s32 {
+  w : Wrap = xx 7;
+  print("w.v = {}\n", w.v);
+  0;
+}