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/0811-modules-same-name-error-set-ambiguous/a.sx

@@ -0,0 +1,4 @@
+// One of two flat-imported authors of a same-name `IoErr` error set. With both
+// modules flat-visible from a file that authors none itself, every bare reference
+// to the name is genuinely ambiguous.
+IoErr :: error { Disk, Net }

examples/modules/0811-modules-same-name-error-set-ambiguous/b.sx

@@ -0,0 +1,4 @@
+// The second flat-imported author of a same-name `IoErr` error set. A separate
+// nominal identity from a.sx's `IoErr`, so each bare reference is a real collision
+// the importing source cannot disambiguate.
+IoErr :: error { Disk, Net }