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/0756-modules-same-name-alias-per-source/a.sx

@@ -0,0 +1,4 @@
+// Module A aliases `Id` to `i32`. A bare `Id` in this module resolves to A's
+// alias regardless of B's same-name alias (per-source alias visibility).
+Id :: i32;
+a_val :: () -> i64 { x : Id = 100; y : i64 = xx x; return y; }