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/0703-modules-into-impl-helper.sx

@@ -0,0 +1,12 @@
+// Helper for 93-into-import-scope.sx: declares Wrap + an impl Into for it.
+// No paired tests/expected file — not executed standalone by the runner.
+
+#import "modules/std.sx";
+
+Wrap :: struct { v: i64 = 0; }
+
+impl Into(Wrap) for i64 {
+  convert :: (self: i64) -> Wrap {
+    .{ v = self * 10 }
+  }
+}