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/expected/0719-modules-cli-and-json.stdout

@@ -0,0 +1,10 @@
+cli-group: ok
+cli-command: ok
+cli-index: ok
+cli-flag: ok
+json-members: ok
+json-key0: ok
+json-str: ok
+json-arr-len: ok
+json-arr-2: ok
+=== DONE ===