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/comptime/0600-comptime-run.sx

@@ -0,0 +1,20 @@
+#import "modules/std.sx";
+// this will bake x to be 7 as a global constant
+x :: #run compute(5);
+
+compute :: (v: i32) -> i32 => v + 2;
+
+main :: () {
+    //test
+    y :: #run compute(7);
+    c :: 2;
+    print("hello {}\n", x + y * c);
+}
+
+#run main();
+
+// ** stdout after build **
+// hello 25
+
+// ** stdout after run **
+// hello 25