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/modules/0707-modules-import-dir-scan-order/aaa_uses.sx

@@ -0,0 +1,11 @@
+// Alphabetically FIRST file in the directory. Its own decl uses
+// `MyEnum`, defined in a sibling file (`types.sx`). The directory
+// import pass must register `MyEnum` BEFORE this file's `make_my`
+// is scanned, or `MyEnum` falls back to a placeholder struct and
+// `return .b(42)` fails with "cannot infer enum type".
+
+#import "types.sx";
+
+make_my :: () -> MyEnum {
+    return .b(42);
+}

examples/modules/0707-modules-import-dir-scan-order/types.sx

@@ -0,0 +1,4 @@
+MyEnum :: enum {
+    a;
+    b: i32;
+}