Expose selection endpoint ordering through the libghostty-vt C API so embedders can safely normalize selections whose start and end refs may be reversed. The new APIs report the current order and return a fresh untracked selection with forward or reverse bounds. Selection.Order now uses lib.Enum, matching the existing adjustment enum pattern and keeping the C ABI enum generated from the same Zig source of truth. The new functions are wired through the C API re-export and lib-vt export paths, with coverage for mirrored rectangular selection ordering.