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/platform/1609-platform-add-framework.sx

@@ -0,0 +1,20 @@
+// BuildOptions.add_framework registers an Apple framework at comptime,
+// equivalent to a top-level `#framework "Name"` directive. The advantage:
+// you can gate it with `inline if OS == .ios { ... }` or similar logic,
+// keeping the framework off non-Apple builds.
+
+#import "modules/std.sx";
+#import "modules/build.sx";
+
+configure_build :: () abi(.compiler) {
+    opts := build_options();
+    opts.add_framework("CoreFoundation");
+}
+#run configure_build();
+
+CFAbsoluteTimeGetCurrent :: () -> f64 extern;
+
+main :: () -> i32 {
+    t := CFAbsoluteTimeGetCurrent();
+    return if t > 0.0 then 0 else 1;
+}