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/http/expected/1633-http-server.stdout

@@ -0,0 +1,9 @@
+GET 200, keep-alive
+keep-alive reuse ok
+request cap: close + EOF
+POST echo ok
+404 routing ok
+big body grows the buffer and echoes intact
+slow client evicted, healthy client served
+pooled dispatch: GET, echo, 404 across worker threads ok
+http server ok