feat: add 'H' toggle to hide completed/scrapped beans in TUI

[matleh]

Refs: beans-k5mz

Summary

• Adds 'H' (shift+h) key binding to toggle visibility of completed/scrapped beans in the TUI
• Uses existing GraphQL ExcludeStatus filter
• Works independently from tag filter - both can be active simultaneously
• List title shows active filters: [hiding completed]
• Changed from 'h' to 'H' to avoid conflict with vim navigation keys

Implementation Details

• Added hideCompleted boolean field to listModel struct
• Modified loadBeans() to use GraphQL ExcludeStatus filter when toggle is active
• Added toggleHideCompleted() method to flip the state
• Implemented 'H' key binding handler to toggle the filter
• Updated list title to show both tag and hide-completed filters when active
• Added 'H' shortcut to help overlay (? key)
• Updated both View() and ViewConstrained() methods for consistency

Testing

• Verified GraphQL ExcludeStatus filter correctly excludes completed/scrapped beans
• Tested toggle functionality in TUI
• Build successful with no compilation errors

[matleh]

Only after I opened the PR I saw that there is already a different concept at #41 .