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/0741-modules-flat-same-name-bare-pack-winner/b.sx

@@ -0,0 +1,6 @@
+#import "modules/std.sx";
+// b.sx authors its OWN plain `f`. `show_b`'s bare `f()` must dispatch b.f (2),
+// not the first-wins pack winner from a.sx (1). The selector picks b.f; the
+// early pack/comptime dispatch must NOT hijack it with the winner.
+f :: () -> i64 { return 2; }
+show_b :: () { print("b: f() = {}\n", f()); }