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/0727-modules-user-ns-m0/a.sx

@@ -0,0 +1,3 @@
+// Flat author of `ping`; `call_a` binds a.sx's own `ping` (1).
+ping   :: () -> i64 { return 1; }
+call_a :: () -> i64 { return ping(); }

examples/modules/0727-modules-user-ns-m0/b.sx

@@ -0,0 +1,3 @@
+// Second flat author of `ping`; `call_b` binds b.sx's own `ping` (2).
+ping   :: () -> i64 { return 2; }
+call_b :: () -> i64 { return ping(); }

examples/modules/0727-modules-user-ns-m0/m.sx

@@ -0,0 +1,3 @@
+// Imported under a user namespace literally named `__m0`. Reached as
+// `__m0.ping` (99); coexists with the flat `ping` collision.
+ping :: () -> i64 { return 99; }