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/protocols/0820-protocols-same-name-method-own-wins/dep.sx

@@ -0,0 +1,10 @@
+// A flat-imported module authors its OWN `Box { a }`, a DISTINCT nominal from
+// main's same-name `Box { m }`. The protocol method-signature return must NOT bind
+// this one — the disjoint field sets make a wrong binding a hard compile error.
+Box :: struct { a: i32; }
+
+dep_box :: () -> i32 {
+    b : Box = ---;
+    b.a = 9;
+    return b.a;
+}