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/diagnostics/1176-diagnostics-import-parse-error-location.sx

@@ -0,0 +1,13 @@
+// A parse error in an IMPORTED file must be located in THAT file, not the
+// importer. Regression: `import_sources` was wired to the diagnostics only
+// AFTER import resolution finished, so a parse error raised MID-resolution
+// (which aborts before that wiring) could not resolve the imported file's
+// source — the caret fell back to the root file and landed on an unrelated
+// line. The fix wires `import_sources` before resolving and pins the
+// diagnostic's `source_file` + offset to the imported file.
+//
+// The companion's error sits several lines down (after comments) so a caret
+// mislocated against THIS importer would be unmistakable.
+#import "1176-diagnostics-import-parse-error-location/broken.sx";
+
+main :: () {}