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/0731-modules-flat-same-name-closure/a.sx

@@ -0,0 +1,6 @@
+// a.sx authors `pick` returning 1. Imported first → first-wins winner.
+// `from_a_closure` / `from_a_value` take a.sx's own author (own == winner →
+// existing path, byte-for-byte unchanged).
+pick :: () -> i64 { return 1; }
+from_a_closure :: () -> i64 { f := closure(pick); return f(); }
+from_a_value   :: () -> i64 { g : () -> i64 = pick; return g(); }

examples/modules/0731-modules-flat-same-name-closure/b.sx

@@ -0,0 +1,6 @@
+// b.sx authors its OWN `pick` returning 2. Taking `pick` as a value —
+// `closure(pick)` or `g : () -> i64 = pick` — must capture b.sx's author (2),
+// not the first-wins winner from a.sx (1).
+pick :: () -> i64 { return 2; }
+from_b_closure :: () -> i64 { f := closure(pick); return f(); }
+from_b_value   :: () -> i64 { g : () -> i64 = pick; return g(); }