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/0786-modules-same-name-const-own/a.sx

@@ -0,0 +1,3 @@
+// Module A authors its OWN value const `K` (1) and reads it bare.
+K :: 1;
+a_k :: () -> i64 { return K; }

examples/modules/0786-modules-same-name-const-own/b.sx

@@ -0,0 +1,5 @@
+// Module B authors a DIFFERENT same-name value const `K` (2) — a shadow of A's
+// `K`. Each `K` is selected per declaring source, so B's `b_k` reads B's value
+// while A's `a_k` reads A's, never the global last-wins const.
+K :: 2;
+b_k :: () -> i64 { return K; }