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/0541-packs-pack-to-protocol-tuple.sx

@@ -0,0 +1,28 @@
+// Phase 6 — `c.sources = (..sources)`: materialize a pack into a
+// protocol-typed tuple field, erasing each concrete pack element to the field's
+// protocol slot. The pack `..sources: VL` holds concrete cells; `(..sources)`
+// into a `(..VL(Ts))` field `xx`-erases each to its `VL(Ti)` value.
+
+#import "modules/std.sx";
+
+VL :: protocol(T: Type) { get :: () -> T; }
+IntCell :: struct { v: s64; }
+StrCell :: struct { s: string; }
+impl VL(s64) for IntCell { get :: (self: *IntCell) -> s64 => self.v; }
+impl VL(string) for StrCell { get :: (self: *StrCell) -> string => self.s; }
+
+Combined :: struct($R: Type, ..$Ts: []Type) {
+    sources: (..VL(Ts));
+    value:   $R;
+}
+
+build :: (..sources: VL) -> void {
+    c : Combined(s64, ..sources.T) = ---;
+    c.sources = (..sources);                          // pack → tuple, per-element erase
+    print("{} {}\n", c.sources.0.get(), c.sources.1.get());
+}
+
+main :: () -> s32 {
+    build(IntCell.{ v = 10 }, StrCell.{ s = "hi" });   // 10 hi
+    0;
+}