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/0752-modules-same-name-struct-distinct-fields/b.sx

@@ -0,0 +1,5 @@
+// Module B authors a DIFFERENT `Box` (two fields `p`, `q`) — a same-name shadow
+// of A's `Box`. Pre-0105 the two collapsed last-wins in the type table, so one
+// module's field set vanished; now each `Box` is a distinct nominal type.
+Box :: struct { p: i64; q: i64; }
+b_box :: () -> Box { return Box.{ p = 3, q = 4 }; }