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/0798-modules-same-name-union-own-wins/dep.sx

@@ -0,0 +1,10 @@
+// A flat-imported module authors its OWN `Pair { a }`. The importing file (`main`)
+// ALSO authors a `Pair` — its own author must win there (own-wins), while this
+// module's `Pair` stays a DISTINCT nominal type used by `dep_pair`. The field sets
+// are disjoint, so a cross-binding to the wrong `Pair` is a hard compile error.
+Pair :: union { a: i32; }
+dep_pair :: () -> i32 {
+    p : Pair = ---;
+    p.a = 9;
+    return p.a;
+}