cursor: add scroll wheel support for window cycle

When cycle mode is active (Alt+Tab held), scrolling the mouse wheel
cycles through windows. Scroll down advances to the next window,
scroll up goes to the previous window.

This uses the same LAB_CYCLE_DIR_FORWARD/BACKWARD constants as the
keyboard handler, ensuring consistent navigation behavior.

No configuration needed - always active during cycle mode.

docs/scroll-cycle.md

@@ -0,0 +1,29 @@
+# Scroll Wheel Support for Window Cycle (Alt+Tab)
+
+## Summary
+
+Add mouse scroll wheel support to the Alt+Tab window switcher. When cycle mode is active (Alt+Tab held), scrolling the mouse wheel cycles through windows — scroll down for next, scroll up for previous.
+
+## Usage
+
+1. Press and hold **Alt+Tab** to enter cycle mode
+2. **Scroll wheel down** → cycle to the next window
+3. **Scroll wheel up** → cycle to the previous window
+4. Release **Alt** to focus the selected window
+
+No configuration needed — this behavior is always active during cycle mode.
+
+## Technical Details
+
+The patch intercepts `WL_POINTER_AXIS_VERTICAL_SCROLL` events in `handle_axis()` when `server.input_mode == LAB_INPUT_STATE_CYCLE`. It maps:
+
+- Negative delta (scroll up) → `LAB_CYCLE_DIR_BACKWARD`
+- Positive delta (scroll down) → `LAB_CYCLE_DIR_FORWARD`
+
+These are the same direction constants used by the keyboard handler (`handle_cycle_view_key()` in `keyboard.c`), ensuring consistent behavior between keyboard and mouse navigation.
+
+The event is consumed (not forwarded to clients or processed as mouse bindings) when cycle mode is active.
+
+## Files Changed
+
+- `src/input/cursor.c` — Added scroll wheel interception in `handle_axis()`

src/input/cursor.c

@@ -1441,6 +1441,17 @@ handle_axis(struct wl_listener *listener, void *data)
 	idle_manager_notify_activity(seat->wlr_seat);
 	cursor_set_visible(seat, /* visible */ true);
 
+	/* Cycle mode: scroll wheel cycles through windows */
+	if (server.input_mode == LAB_INPUT_STATE_CYCLE) {
+		if (event->orientation == WL_POINTER_AXIS_VERTICAL_SCROLL
+				&& event->delta != 0) {
+			cycle_step(event->delta < 0
+				? LAB_CYCLE_DIR_FORWARD
+				: LAB_CYCLE_DIR_BACKWARD);
+		}
+		return;
+	}
+
 	/* input->scroll_factor is set for pointer/touch devices */
 	assert(event->pointer->base.type == WLR_INPUT_DEVICE_POINTER
 		|| event->pointer->base.type == WLR_INPUT_DEVICE_TOUCH);