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/protocols/expected/0403-protocols-protocol-dispatch-via-fn-arg.stdout

@@ -0,0 +1,8 @@
+=== Direct 1 ===
+r1 = 42
+=== Direct 2 ===
+r2 = 42
+=== From function ===
+dispatch_fn: about to dispatch
+dispatch_fn: result = 42
+=== OK ===