Mouse scrolling no longer works after removing tmux

[goudyj]

Context
Since the migration away from tmux for session management, mouse scrolling has stopped working in the TUI. The scrolling functionality was likely tied to tmux's terminal handling and needs to be reimplemented for the new direct PTY approach.

Steps to reproduce

1. Launch the application (post-tmux removal).
2. Navigate to a view with scrollable content (e.g., issue list).
3. Attempt to scroll using the mouse wheel.
4. Observe that scrolling does not respond.

Expected behavior
Mouse wheel scrolling should navigate through scrollable content in the TUI sessions.

Actual behavior
Mouse scroll events are ignored; the view does not scroll.

Technical notes

• Review how mouse events are captured and processed in the new PTY-based session handling.
• Ensure mouse capture mode is enabled for the terminal.
• Check if scroll events need to be explicitly forwarded to the active session/widget.