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/0049-basic-defer-break-continue.stdout

@@ -0,0 +1,18 @@
+body 0
+cleanup 0
+cleanup 1
+after break loop
+b2 0
+c2 0
+c2 1
+b2 2
+c2 2
+done
+wbody1
+w1
+w2
+w3
+while done
+inner 0
+outer 0
+nested done