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/0761-modules-imported-generic-undeclared-field/lib.sx

@@ -0,0 +1,12 @@
+// Flat-imported generic struct with a genuinely-undeclared field type
+// (`y: Missing`). 0759 covers a NON-generic imported struct; a generic one is
+// instantiated cross-module, so before the fix its field nodes were resolved in
+// the (main-file) instantiation context — the source-aware leaf saw "main",
+// trusted it to the `UnknownTypeChecker` (which never walks imports), and
+// silently fabricated a 0-field stub. `instantiateGenericStruct` now resolves
+// the template's fields in THIS module's source context, so the undeclared name
+// surfaces at the reference.
+Bad :: struct($T: Type) {
+    x: T;
+    y: Missing;
+}