chore: Add better error handling using ErrorPopup

[ekideno]

Refactored error handling across the codebase to use the existing ErrorPopup component via utils.ReturnError() function. This provides a consistent user experience when errors occur in the TUI.

Changes:

• Updated internal/models files to return errors from Update() methods using utils.ReturnError() which displays errors via ErrorPopup
• Modified file operation handlers (create, delete, rename, move) to return errors instead of calling os.Exit(1)
• Updated daily task operations (GetItems, WriteItems, handlers) to propagate errors properly
• Fixed viewer ReadFile() to return errors instead of printing them
• Updated constructors (NewDaily, NewHome, NewFileExplorer) to return errors for proper initialization error handling
• Improved CLI commands to return errors using standard Go error handling

All error handling now follows the pattern specified in issue #63: utils.ReturnError() is only called from Update() methods, and errors are properly propagated through the call chain.

Fixes #63