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/0738-modules-comptime-arg-caller-context/emit.sx

@@ -0,0 +1,9 @@
+// Library metaprogram: builds a `print(...)` statement at compile time from the
+// comptime `$who` value. `concat`/`print` are flat-imported here and resolve in
+// THIS module's context (the 0106 defining-module pin). The substituted caller
+// `$`-arg, by contrast, resolves in the CALLER's context.
+#import "modules/std.sx";
+
+emit :: ($who: string) {
+    #insert concat(concat("print(\"hello ", who), "\\n\");");
+}