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/comptime/expected/0608-comptime-comptime.stdout

@@ -0,0 +1,9 @@
+=== 8. Comptime ===
+run-const: 25
+run-expr: 42
+run-chain: 30
+ct-opt-coalesce: 141
+ct-opt-unwrap: 77
+ct-opt-guard: 10
+insert-ok
+insert-gen: 42