feat(ui): Add stack view resize on screen size change

[mhiro2]

Summary

• Add resize_all() function to stack view module to handle window resize events (VimResized/WinResized)
• Integrate resize_all() call into debounced reflow events for automatic resizing
• Add comprehensive tests for layout edge cases and reflow behavior
• Ensure reflow_all safely skips hidden stacks without error

Changes

• 8643ccb : feat(ui): add stack view resize on screen size change
  • Add resize_all() function to stack_view/init.lua that updates window config for all open stack views
  • Call resize_all() in events.lua during debounced reflow to respond to screen size changes
  • Add tests for layout clamping to min_size on small screens, non-negative position validation, and reflow
    behavior