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/1605-platform-frameworks.sx

@@ -0,0 +1,12 @@
+// `#framework "Name"` top-level directive registers an Apple framework for
+// linking; `extern` declarations can omit the library identifier (frameworks
+// resolve symbols by global namespace at link time).
+
+#framework "CoreFoundation";
+
+CFAbsoluteTimeGetCurrent :: () -> f64 extern;
+
+main :: () -> i32 {
+    t := CFAbsoluteTimeGetCurrent();
+    return if t > 0.0 then 0 else 1;
+}