test: group examples into per-category folders

Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.

examples/types/0128-types-tuples.sx

@@ -0,0 +1,27 @@
+#import "modules/std.sx";
+#import "modules/math";
+#import "modules/build.sx";
+#import "modules/std/test.sx";
+pkg :: #import "tests/fixtures/testpkg";
+
+main :: () {
+
+    // --- Tuples ---
+    {
+        print("=== Tuples ===\n");
+        pair := (40, 2);
+        print("{}\n", pair.0);
+        print("{}\n", pair.1);
+
+        named := (x: 10, y: 20);
+        print("{}\n", named.x);
+        print("{}\n", named.0);
+
+        single := (42,);
+        print("{}\n", single.0);
+
+        zeroed : (i32, i32) = ---;
+        print("{}\n", zeroed.0);
+        print("{}\n", zeroed.1);
+    }
+}