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/0753-modules-same-name-struct-same-fields/b.sx

@@ -0,0 +1,5 @@
+// Module B authors `Pair { x, y }` with the SAME field shape as A's. The two
+// still get distinct nominal identities (not collapsed): each keeps its own
+// TypeId / per-source author, so both register and format independently.
+Pair :: struct { x: i64; y: i64; }
+b_pair :: () -> Pair { return Pair.{ x = 5, y = 6 }; }