feat: add configurable diff modes and split orientation

src/main.rs

@@ -69,6 +69,8 @@ Diff: :diff (Normal); choose Before then After; Working checkout After edits liv
       Switching Before/After preserves the aligned cursor row and display column
       Selector queries own printable keys, including :; text navigation skips omitted lines
       Normal [/] explicitly expands context; Insert brackets remain literal text
+      Normal Space v cycles split/unified; Space s flips left/right vs above/below split
+      Defaults: config.diff_view_mode = \"split\"; config.diff_split_orientation = \"left_right\"
       Esc closes Before/After selectors; :diff.close exits an opened comparison explicitly
       Remote refs/history load into temporary comparison repos without changing active refs/checkout
       Changed files: normal picker/explorer bindings, Ctrl+w close; A/M/D/R status and rename paths