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/0100-types-structs.sx

@@ -0,0 +1,36 @@
+#import "modules/std.sx";
+Vec4 :: struct {
+    x, y, z, w: f32;    
+}
+
+Complex :: struct {
+    foo : enum {
+        S: s32;
+        B: struct {
+            val: string;
+        };
+    } = .B.{"hello"};
+}
+
+main :: () {
+    v1 : Vec4 = .{ 1, 2, 3, 0};
+    v2 := Vec4.{ 4, 1, 1, 3};
+    v3 := Vec4.{ w=0, x=2, y=3, z=4};
+    z := 5.0; // z is f32
+    w := 6.0; // w is f32
+    v4 := Vec4.{ y=3, x=9, w, z};
+
+    v4.y = 0;
+    print("v1: {}\nv2: {}\nv3: {}\nv4: {}\n", v1, v2, v3, v4);
+
+    complex : Complex = .{};
+    print("\n{}\n", complex);
+}
+
+// ** stdout **
+//v1: Vec4{x:1.0, y:2.0, z:3.0, w:0.0}
+//v2: Vec4{x:4.0, y:1.0, z:1.0, w:3.0}
+//v3: Vec4{x:2.0, y:3.0, z:4.0, w:0.0}
+//v4: Vec4{x:9.0, y:3.0, z:5.0, w:6.0}
+//
+//Complex{foo: .B(Complex.foo.B{val: hello})}