Cycle focused window through tiles (⌃⌥Tab)

[m96-chan]

Summary

Add a keyboard shortcut (⌃⌥Tab) to cycle the currently focused window through available leaf tiles, one step at a time.

Motivation

Repositioning a window across tiles currently requires either Shift+Drop (mouse) or the move hotkeys (⌃⌥⇧Arrow), which depend on spatial adjacency. A cycle shortcut lets the user quickly relocate a window without knowing the exact tile layout — just keep pressing ⌃⌥Tab until it lands where you want.

Proposed Behavior

• ⌃⌥Tab: move the focused window to the next leaf tile (wraps around)
• ⌃⌥⇧Tab: move to the previous leaf tile (reverse direction)
• Leaf tile order follows the tree traversal order (left-to-right, top-to-bottom)
• Works across all tiles on the focused window's display

Scope

• Add `cycleWindowNext` and `cycleWindowPrev` to `HotkeyAction`
• Add default bindings ⌃⌥Tab / ⌃⌥⇧Tab to `HotkeyManager.defaultBindings`
• Implement cycle logic in `AppCoordinator.handleAction`
• Expose in Preferences → Keyboard Shortcuts (automatic, same as other actions)

Notes

Tab key code: kVK_Tab = 48. The ⌃⌥Tab combination should not conflict with standard macOS shortcuts.