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/0838-memory-helpers.stdout

@@ -0,0 +1,9 @@
+create: 7 42
+pipe-create: 1
+dot-create: 2
+alloc: 10 40 len=4
+clone: 10 (orig 99)
+resize: 20 60 len=6
+shrink: 99 20 len=2
+realloc: 1234
+TrackingAllocator: allocs=8 deallocs=8 outstanding=0 total_alloc_bytes=184