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/basic/expected/0029-basic-scoping.stdout

@@ -0,0 +1,23 @@
+=== 6. Scoping ===
+inner: 200
+outer: 100
+shadow-type: 42
+shadow-type: 3.140000
+nest3: 3
+nest2: 2
+nest1: 1
+scope-isolate: 100
+scope-reuse: 1
+scope-reuse: 2
+scope-reuse: 1
+defer-a
+defer-b
+defer-c
+d4
+d3
+d2
+d1
+inner-defer
+outer-defer
+defer-in-if: body
+defer-in-if: deferred