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/0814-modules-same-name-error-set-lambda-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, the `-> !IoErr`
+// closure-literal channel is genuinely ambiguous.
+IoErr :: error { Disk, Net }