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/0730-modules-flat-same-name-default-arg/a.sx

@@ -0,0 +1,5 @@
+// a.sx authors `cfg` defaulting to 10. Imported first, so it is the first-wins
+// merge winner. `from_a` calls `cfg()` with the arg omitted — own == winner →
+// existing default-expansion path, byte-for-byte unchanged.
+cfg    :: (n: i64 = 10) -> i64 { return n; }
+from_a :: () -> i64 { return cfg(); }

examples/modules/0730-modules-flat-same-name-default-arg/b.sx

@@ -0,0 +1,5 @@
+// b.sx authors its OWN `cfg` defaulting to 20. `from_b`'s `cfg()` omits the
+// arg; the omitted trailing default must come from b.sx's author (20), not the
+// first-wins winner from a.sx (10).
+cfg    :: (n: i64 = 20) -> i64 { return n; }
+from_b :: () -> i64 { return cfg(); }