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/0789-modules-same-name-const-leaf-author-pin/a.sx

@@ -0,0 +1,5 @@
+// Module A authors `M :: 1` and the EXPRESSION const `K :: M + 1` (= 2). `K` is
+// unique across the program; only A defines it. Its RHS leaf `M` must always
+// fold against A's `M` (= 1), no matter which module reads `K`.
+M :: 1;
+K :: M + 1;

examples/modules/0789-modules-same-name-const-leaf-author-pin/b.sx

@@ -0,0 +1,5 @@
+// Module B authors only a DIFFERENT same-name `M :: 10` — a shadow of A's `M`,
+// with NO `K`. When `main` flat-imports both A and B, the reading module sees
+// two `M`s; folding A's `K :: M + 1` must NOT use this `M` (which would make `M`
+// ambiguous from the reader's view) — it must pin to A's `M`.
+M :: 10;