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/0703-modules-into-import-scope.sx

@@ -0,0 +1,13 @@
+// Phase 4 (xx-via-Into mechanism): an `impl Into(...) for ...` lives in
+// a separate file and reaches the xx site through a direct `#import`.
+// The visibility filter accepts the impl because the user file
+// transitively imports the impl's defining module.
+
+#import "modules/std.sx";
+#import "./0703-modules-into-impl-helper.sx";
+
+main :: () -> i32 {
+  w : Wrap = xx 3;
+  print("w.v = {}\n", w.v);
+  0
+}