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/0721-modules-qualified-terminating-callee/helper.sx

@@ -0,0 +1,3 @@
+// Lives in m.sx's OWN flat import — reachable from `foo` but not from the
+// top-level consumer that imports m.sx under a qualified namespace.
+helper :: () -> i64 { return 7; }

examples/modules/0721-modules-qualified-terminating-callee/m.sx

@@ -0,0 +1,10 @@
+// `foo` is pulled in QUALIFIED by the consumer (`m :: #import …`). Its body
+// terminates via a constant-folded `if true { return … }`, and the `return`
+// calls `helper` from m.sx's OWN flat import. Lowering `foo` as a qualified
+// alias must be transparent to the caller's lowering state — issue 0100 F2.
+#import "helper.sx";
+
+foo :: () -> i64 {
+    if true { return helper(); }
+    return 0;
+}