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/0722-modules-flat-same-name-own/b.sx

@@ -0,0 +1,4 @@
+// b.sx authors its OWN `greet`. `from_b`'s bare `greet` must bind b.sx's
+// author (2), not the first-wins winner from a.sx.
+greet  :: () -> i64 { return 2; }
+from_b :: () -> i64 { return greet(); }