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/1617-modules-library-nested-namespace.sx

@@ -0,0 +1,10 @@
+// Regression (issue 0130): a #library declared in a module reached through
+// TWO aliased imports must still be linked (AOT) / dlopened (JIT).
+#import "modules/std.sx";
+b :: #import "1617-modules-library-nested-namespace/b.sx";
+
+main :: () -> i32 {
+    v := b.version_via_b();
+    print("pcap version non-empty: {}\n", v.len > 0);
+    return 0;
+}