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/0750-modules-forward-alias-source-aware/dep.sx

@@ -0,0 +1,10 @@
+// Namespaced helper module. It authors a top-level type alias `B` whose
+// spelling collides with the importer's own `B`. Because the import is
+// NAMESPACED (`ns :: #import`), `dep.B` is NOT flat-visible to the importer —
+// but its alias write still lands in the global `type_alias_map` (last-wins),
+// which is exactly what the source-aware forward-alias fixpoint must ignore.
+B :: u8;
+
+width :: () -> i32 {
+    return 8;
+}