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/0791-modules-same-name-const-multi-level-cross-module/c.sx

@@ -0,0 +1,5 @@
+// Module C flat-imports A only and authors `BIG :: K + 100`. Its bare `K` is A's
+// (= 2), so `BIG` folds to 102. The leaf must pin to A across the import into
+// `main`, which itself sees a different same-name `K` (B's = 11).
+#import "a.sx";
+BIG :: K + 100;