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/0827-protocols-param-impl-source-wrapped-ambiguous/a.sx

@@ -0,0 +1,9 @@
+// One of two flat-imported `Box` authors; with no own author the param-impl
+// SOURCE `*Box` is a genuine collision.
+Box :: struct { a: i32; }
+
+a_box :: () -> i32 {
+    b : Box = ---;
+    b.a = 1;
+    return b.a;
+}

examples/protocols/0827-protocols-param-impl-source-wrapped-ambiguous/b.sx

@@ -0,0 +1,8 @@
+// The second flat-imported `Box` author — a DISTINCT nominal from a.sx's `Box`.
+Box :: struct { b: i32; }
+
+b_box :: () -> i32 {
+    x : Box = ---;
+    x.b = 2;
+    return x.b;
+}