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/modules/expected/0711-modules-sha256-vectors.stdout

@@ -0,0 +1,15 @@
+empty: ok
+abc: ok
+nist-56: ok
+nist-112: ok
+len-0: ok
+len-55: ok
+len-56: ok
+len-57: ok
+len-63: ok
+len-64: ok
+len-65: ok
+len-119: ok
+len-120: ok
+a-1000: ok
+a-1000000: ok