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/0726-modules-flat-same-name-variadic/a.sx

@@ -0,0 +1,11 @@
+// a.sx is the first-wins winner for both names. `combine` is FIXED arity;
+// `pick` is VARIADIC. `from_a_*` call them bare — a authors the winner, so
+// they resolve through the existing path and pack against a's own shapes.
+combine :: (x: i64, y: i64) -> i64 { return x + y; }
+pick :: (..xs: []i64) -> i64 {
+    result := 0;
+    for xs (it) { result = result + it; }
+    result
+}
+from_a_combine :: () -> i64 { return combine(10, 20); }
+from_a_pick :: () -> i64 { return pick(1, 2, 3); }