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/0410-protocols-impl-visibility-user.sx

@@ -0,0 +1,10 @@
+// User file uses xx but only imports the shared types — NOT the impl.
+// The Phase 4 visibility filter should reject the impl from 179-impl-visibility-impl.sx.
+#import "modules/std.sx";
+#import "./0410-protocols-impl-visibility-types.sx";
+
+run_user :: () -> i32 {
+  w : Wrap = xx 7;
+  print("user: w.v = {}\n", w.v);
+  0
+}