feat: WindowSwitcherPrev action with super+shift+tab default binding

Reverse companion to window_switcher: cycles the switcher highlight
backwards. Ships as a stock default chord so it works without an
input.kdl entry (defaults never shadow user bindings).

Co-Authored-By: Claude Fable 5 <[email protected]>

 src/api.rs      | 3 +++
 src/bindings.rs | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/api.rs b/src/api.rs
index 4adf21b..442e9e5 100644
--- a/src/api.rs
+++ b/src/api.rs
@@ -56,6 +56,7 @@ pub enum Action {
     FocusLeft,
     FocusRight,
     WindowSwitcher,
+    WindowSwitcherPrev,
     Move,
     Resize,
     Exit,
@@ -101,6 +102,7 @@ impl Action {
             Action::FocusLeft => "focus_left",
             Action::FocusRight => "focus_right",
             Action::WindowSwitcher => "window_switcher",
+            Action::WindowSwitcherPrev => "window_switcher_prev",
             Action::Move => "move",
             Action::Resize => "resize",
             Action::Exit => "exit",
@@ -146,6 +148,7 @@ impl Action {
             "focus_left" => Action::FocusLeft,
             "focus_right" => Action::FocusRight,
             "window_switcher" => Action::WindowSwitcher,
+            "window_switcher_prev" => Action::WindowSwitcherPrev,
             "move" => Action::Move,
             "resize" => Action::Resize,
             "exit" => Action::Exit,
diff --git a/src/bindings.rs b/src/bindings.rs
index c348c1e..6935282 100644
--- a/src/bindings.rs
+++ b/src/bindings.rs
@@ -148,6 +148,8 @@ pub const DEFAULT_BINDINGS: &[DefaultBinding] = &[
     DefaultBinding { mods: mods::SUPER | mods::CTRL, key: "minus", action: Action::ZoomOut },
     DefaultBinding { mods: mods::SUPER | mods::CTRL, key: "equal", action: Action::ZoomReset },
     DefaultBinding { mods: mods::SUPER | mods::SHIFT, key: "r", action: Action::Reload },
+    // Reverse companion to the (user-configured) super+tab window switcher.
+    DefaultBinding { mods: mods::SUPER | mods::SHIFT, key: "Tab", action: Action::WindowSwitcherPrev },
 ];
 
 #[cfg(test)]
@@ -182,7 +184,7 @@ mod tests {
             Action::None, Action::Spawn, Action::Toggle, Action::Close,
             Action::FocusNext, Action::FocusPrev, Action::FocusUp,
             Action::FocusDown, Action::FocusLeft, Action::FocusRight,
-            Action::WindowSwitcher,
+            Action::WindowSwitcher, Action::WindowSwitcherPrev,
             Action::Move, Action::Resize, Action::Exit, Action::Reload,
             Action::Fullscreen, Action::LayoutNext, Action::ModeNext,
             Action::ModeNextShared, Action::View1, Action::View2,