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/errors/1013-errors-value-failable-reject.sx

@@ -0,0 +1,19 @@
+// Value-carrying `catch` rejection (ERR step E2.1b): when the failable LHS
+// carries a value, a non-diverging catch handler must produce a value of the
+// success type — a value-less (void) body is a type error (otherwise the
+// success and error paths couldn't merge to one value). Diverge instead
+// (`return` / `raise`) or yield a value. Positives: `examples/229-value-failable-consume.sx`.
+
+#import "modules/std.sx";
+
+E :: error { Bad }
+
+parse :: (n: i32) -> (i32, !E) {
+    if n < 0 { raise error.Bad; }
+    return n;
+}
+
+main :: () -> i32 {
+    x := parse(-1) catch (e) { print("oops\n") };   // error: body yields no value
+    return x;
+}