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/memory/expected/0802-memory-pointers.stdout

@@ -0,0 +1,5 @@
+before: Vec2{x: 1.000000, y: 2.000000}
+after: Vec2{x: 99.000000, y: 2.000000}
+copy: Vec2{x: 99.000000, y: 2.000000}
+mp[0] = 10
+mp[2] = 30