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/1008-errors-match-diverging-arms.sx

@@ -0,0 +1,40 @@
+// Regression for issue 0057: a match (`if subject == { case ... }`) whose arms
+// ALL diverge (each `return`s) used to fail LLVM verification (a `void` phi +
+// "terminator in the middle of a basic block") — lowerMatch emitted a
+// value-merge phi and a fallback `const` into arm blocks that had already
+// terminated. Now a fully-diverging match produces no merge phi, and a mixed
+// match (some arms diverge, some yield values) materializes the merge only
+// from the value-producing arms.
+
+#import "modules/std.sx";
+
+// All arms diverge — the match is `noreturn`, no merge phi.
+classify :: (n: s32) -> s32 {
+    if n == {
+        case 0: return 10;
+        case 1: return 20;
+        else:   return 90;
+    }
+    return 0;                       // unreachable
+}
+
+// Mixed: value arms + a diverging arm.
+pick :: (n: s32) -> s32 {
+    v := if n == {
+        case 0: 1;
+        case 1: return 100;         // diverging arm — no fallback const after its `ret`
+        else:   3;
+    };
+    return v + 5;
+}
+
+main :: () -> s32 {
+    r : s32 = 0;
+    r = r + classify(0);            // 10
+    r = r + classify(1);            // 20
+    r = r + classify(7);            // 90
+    r = r + pick(0);                // 1 + 5 = 6
+    r = r + pick(9);                // 3 + 5 = 8  (else arm)
+    print("match result: {}\n", r); // 10+20+90+6+8 = 134
+    return r;
+}