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/0831-modules-namespace-alias-carry/facade.sx

@@ -0,0 +1 @@
+r :: #import "rich.sx";

examples/modules/0831-modules-namespace-alias-carry/rich.sx

@@ -0,0 +1,9 @@
+Thing :: struct {
+    v: i64;
+    init :: () -> Thing { Thing.{ v = 5 } }
+    get :: (self: *Thing) -> i64 { self.v }
+}
+Color :: enum { red; green; }
+LIMIT :i64: 99;
+Box :: struct ($T: Type) { item: T; }
+helper :: () -> i64 { 7 }