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/0700-modules-import.sx

@@ -0,0 +1,17 @@
+std :: #import "modules/std.sx";
+
+//flat
+#import "modules/math";
+
+main :: () -> i32 {
+    {
+        defer std.print("after hello");
+        //expect stdout : hello there
+        std.print("hello there");
+    }
+
+    v:= std.Vector(3,f32).[1,2,3];
+
+    std.print("\n{}\n", v);
+    0
+}